Well, I'm the one who concluded that Michael (1817-1878) was an otherwise unrecorded son of John Toothman and Sarah Windsor, so will try to explain the rationale. I overlooked this query previously, for which I apologize. I was on full-time care-giver duty at the time. Most of this is from memory, with some access to my database, but the notes there don't always give the details of the evidence I worked with -- I was doing it for my own information and remembered the processes pretty well.
The 1820 and 1830 censuses show a male of Michael's approximate age in John Toothman's household, who is not otherwise identifiable. John also had sons named Enoch and Eli, who are not documented in any known source. One of my high school teachers was married to a great-granddaughter of John "Jack" Toothman JR (c1828-1912). He wasn't particularly interested in Toothman genealogy but told me that Jack had brothers named Enoch and William. The suretor on Enoch's marriage bond was Dudley Windsor, Sarah's brother, and a male of this age is found in John Toothman's household, on the censuses which only name the householder. Enoch was a storekeeper who bankrupted in the early 1850s and moved to MO, later to TX. He had no known later contact with WV, except when his children sold their interest in lands inherited through their mother. He doesn't fit anywhere else, and I have assigned him to the John Toothman family, as it is very hard to put him anywhere else.
Eli Toothman, b c1825, also fits into John's household on the 1830 and 1840 censues, though I don't know of a document which puts him there. He, and I think two of John's daughters, were witnesses in a lawsuit of the mid-1840s in Marion Co, involving their neighbor Marcus Millan. I've only seen what is labeled as "Witness Book," lists of subpoenas in various cases; AFAIK there is no case file. Eli was living in Barbour Co, WV, by 1850, with wife Harriet, unidentified. In 1860 they are living at Evansville, Preston Co, a few miles north. Both disappear after 1860, Eli perhaps dead. They had no known issue.
John Toothman's family is the one most closely associated with Barbour Co, which had several families who had come from the same neighborhood as the Toothmans, along the Mason Dixon Line in Allegany Co, MD/Bedford Co, PA. Henry Valentine married Matilda Toothman. The Valentines are part of the same extended family as the Rices (Reiss), who have traveled in America with the Toothmans for 250 years and before that time lived in a town about 3/4 mile away from the Toothman anceestors (however, they are of no discernable relationship to each other overseas, barring, perhaps, that of Adam and Eve).
Joanna Toothman married 1st, Peter Poling, 2nd Richard Pitzer. Poling was from Barbour Co, while Pitzer was from Marion but closely related to the Pitzers in Barbour Co. Pitzer's previous wife had been Mary Rice, dau of Isaac Rice and his unknown first wife. Isaac was the son of Andrew Rice Sr (Andreas Reiss, 1738-1816) of Allegany Co.
In the early 1850s, I believe it was, John Toothman Sr conveyed his land on Bethel Run to his son John Jr. He retained a lifetime right of residence for himself and his wife. He may have paid legacies to his other children with the proceeds or he may have had title bonds with Jack for the son to do so; it's not in the deed itself. Sarah died in 1859. John and Jack apparently fell out soon after, and in 1860 John, age 82, is found living with Eli Toothman in Preston Co, WV. This tends to support the idea that Eli was John's son, and that Eli either died before 1870 or decided to move west and was unable to take the old man with him. In 1870 John is living with his son-in-law Richard Pitzer at Bethel. Pitzer made a will in the early 1870s, which requests that in the event of his own death, one of "Father Toothman's" sons will take care of the old man. However, John died in 1876, age 97, and Pitzer added a codicil noting that "the Lord has called Father Toothman home" and canceling the request in his will. (NB that at the time Pitzer made his will, only 2 of John sr's sons were still living in WV: William "J" and John.)
I have never found any trace of Michael (1817-1878) in local records. He married in Greene Co, PA, I believe -- at least, that's where his wife was born -- and was living by 1850 in Coshocton Co, OH. (Your query says they m in Coshocton, which probably means Michael went directly there, but he had relations in the county.) Michael Toothman Sr, the uncle of John Sr, had gone from Monongalia to Coshocton somewhere around 1816. Andrew Toothman, the younger, probably half-, brother of John Sr also lived in Coshocton, though he came back to WV to die in his old age. Urias Toothman, 1836-1865, son of William "J" Toothman (son of John Sr), was farmhanding a county or so below Coshocton in 1860. (The family of Michael Toothman Sr is also hazy and is reconstructed through circumstantial clues.)
This is the link which connects Michael (1817-1878) to John Toothman Sr. I had never encountered Michael at all until I came into contact with descendants of Eli Newton Valentine, 1853-1938. They reported that Eli had gone west with the family of Michael Toothman and Hannah Phillips, but were hazy as to the relationship between them, though they knew there was one. A county history gave Eli's parents as Henry Valentine and Elisabeth Toothman. This is not the Henry who married John Toothman's daughter Mathilda. Eli's father was Henry Valentine, 1817-1892, of Marion Co, WV. He was the son of Adam Valentine and Elisabeth Rice, and lived on a farm adjoining that of William Rice, Elisabeth's brother, and his wife Eva, who was almost certainly Eva Valentine, sister of Adam Valentine. Henry married Ellen Hoult in 1848 but they separated and did not live together again. There was no issue. In 1850 Henry is living alone. In 1853 he reports the birth of Newton Toothman, son of Elisabeth Toothman. John Toothman had a daughter Elisabeth, born abt 1823, disappears, perhaps dead, by 1860; the only loose Elisabeth known at this time, so she's probably the mother. I had noted that John Toothman Sr is living in 1860 with Eli Toothman, of Preston Co, WV. Also in the household is Eli N Vallentine, age 7. This is certainly Elisabeth's son, and his presence in this context points to his being John Sr's grandson.
Henry Valentine did not marry again until 1867, after the death of his first wife Ellen Hoult. He married Marcella Wade, 1839-1925, daughter of Daniel Wade and Juliana Toothman of Monongalia Co. Juliana was the daughter of John Toothman and Sarah Windsor. Henry was not married to Elisabeth Toothman and did not acknowledge her son Eli. The division of his estate was made among Marcella and their three children.
Thirty some years ago I was in touch with some Michael Toothman descendants who understood that he was the son of Enoch Toothman and grandson of Levi Toothman. Enoch, of course, was his brother's name, and Levi is misplaced from his father-in-law, Levi Phillips. Enoch, c1813-bef 1881, is the first of that name in the family. The only early Levi was b abt 1820 and was the son of John Sr's younger half-brother Christian Toothman. There have been a couple of Levis since then, all I think in the Christian line. Even though the names are wrong, they're specific enough to point to the correct alignment. With that, and the Eli Valentine association, I believe the circumstantial evidence leads to the conclusion that Michael Toothman is the unidentified male in this age range on 1820 and 1830 censuses for John Toothman Sr.
If a family Bible record existed, its whereabouts are unknown today, and due to John Sr's disposal of his real estate during his life, there was no need for him to make a will or for his personal estate to enter probate. So there is no official full record of his family. As in some of the other Toothman families, you have to use circumstantial clues and process of elimination to fill in some of the households. My reconstructino of the John Toothman family is as per:
1. Ara Jane Toothman, b abt 1806, married Barnett Poling of Barbour Co, WV. (Marriage bond.)
2. William J Toothman, 1809-1887, married Mary McDougall, lived Marion Co. (Marriage bond suretor is Dudley Windsor, and his death record gives him as son of John & Sarah.)
3. Joanna Toothman, 1810-1896; married 1st Peter Poling, 2nd Richard Pitzer (marriage bond gives her as dau of John, and he lived with her and Pitzer, who reports John's death as son-in-law).
4. Matilda Toothman, b abt 1812, + ?bef 1862, Ritchie Co, WV. Married Henry Valentine (marriage bond; sketch in 1880s country history of a son also says John Toothman was his grandfather but erroneously states that he was a War of 1812 veteran -- the only known John Toothman with war of 1812 service was the son of Michael Toothman Sr and moved from WV to IN c1816).
5. Enoch Toothman, b c1812, + bef 1881, probably in Kaufman Co, TX. Married Christina Jones, with Dudley Windsor as suretor on the bond. Moved to MO in 1850s, to TX after the Civil War.
6. Juliann Toothman, 1816=1908, married Daniel Wade, lived Monongalia Co. (Marriage bond; family record is in F M Brand, "Wade Family.")
7. Michael Toothman, 1817-1874, married Hannah Phillips (supra)
8. Elisabeth Toothman, c1823-?bef 1860. (1850 census)
9. Eli Toothman, c1825-?bef 1870 (supra)
10. John Toothman Jr "Jack" c1825-1912; m Mary H Billingsley (1850 census, deed from John Sr to John Jr)
11. Eliza Toothman, born c1828, probably the Eliza who was mother of Josephus Toothman, 1847; married, 1854, Simon Madden. Moved out of state?
Dates are usually approximate, mostly from not that satisfactory censuses. Julianne, e.g., is 95 on her death act, calling for birth c1812, though younger on censuses. And either an infant death or one of the later, squeezed-up, births, or both, probably goes into the gap between Michael 1817 and those of the middle 1820s. Chalk this up to inadequate death records and people who rarely put up gravestones because everybody in the family knew who was buried where, and it only took one "I forgot" or "I don't really care" to lose it all.
Hope this clarifies my rationale; when records don't exist whole-family genealogy can help considerably, as it shows yuo where the missing pieces are. Then you search for associations.
The only other plausible background for Michael 1817-1874 would be that he was perhaps an illegitimate son of one of the daughters of Michael Toothman Sr of Coshocton. Michael's sons John, George, and Philip all lived in IN; Philip is a little too young to be the father, as is Michael Jr of Coshocton. He won't go at all into the family of Christian (1764-1823), and there is really nowhere else for him in the family of Diederich (c1750/51-1825). I suppose it's possible that he could have been a son of Andrew (c1786-1870), Diederich's son who went to Coshocton fairly early, but I've never found any evidence that Andrew was married or had issue. In 1850 he was living in the house of Rodger Parks (a Roger Parke married one of the Windsor girls in Monongalia Co, a generation earlier, and this may be a son), with no wife present. Andrew came back to WV after 1860 and lived with the family of his brother Adam until his death in 1870. (His tombstone says he died 1878, age 80, but the 1870 mortality schedule shows him dying in Jan 1870, age 84. He's buried beside some of the children of Adam Toothman who died young.)
But, IMO, the Eli Valentine connection points to Michael being his uncle and therefore a son of John Toothman Sr and Sarah Windsor.