"(In one case, if the age given for one woman in the 1880 census was correct, she would have married at the age of about 13!)"
Yes, some were actually married at ages from 12 - 14.
Anything being done by human beings is subject to errors. The more times it is redone, the more chance for more errors.
Here's a source I've found interesting.http://www.heritagequestonline.com/prod/genealogy/images/cen...
Check out the information on Census Copies, I found info given for 1850-1870 interesting.
also found herehttp://www.genealogybulletin.com/archives/HTML/current29.htm...
Be Aware of Copying Errors!
Harry Hollingsworth reported some differences between the state and federal census copies in his article, "Little Known Facts About the U.S. Census," in the American Genealogist, Vol. 53 (1977), page 11:
" I have personally found many discrepancies between the Federal and State copies . . . Whole names have either been changed or omitted. Ages have been copied wrong. Whereas, in the originals, the surnames of each family are generally written over and over again, in the copies the word "ditto" or its abbreviation "do" appears instead. When written over and over, a surname has much less chance of being written incorrectly! In one Federal entry, I find Rebecca Gey but "Grey" in the original. In anther Federal entry, Amanda Vandyke appears, but she is Amanda A. Vanslyke in the original. Esther Hollinsworth of the original â€” the correct name â€” appears as Esther Hollenback in the Federal copy!"
Genealogist Leland Meitzler discovered what appeared to be his great-grandfather and family listed in the 1860 Wisconsin federal census under the name "Metzern." But by looking at the state copy of the 1860 Wisconsin census, he found the name was spelled correctly as "Meitzler."
There are many more examples of copying errors between the county, state, and federal copies. The original census schedules were bound into large books and the task of copying the handwritten information from one book to another book was obvious tedious and prone to errors.
Knowing that your ancestor were listed in a microfilmed census record and that record may not have been the original â€” does that explain why the name of your ancestor is missing, misspelled, or was given a first letter initial rather than the full name?