Peggy is a common nickname for Margaret, so those two could well be one and the same. And I have seen census records where first names varied considerably, due to personal preferences varying -- or, of course, other reasons such as second wives, etc. Rarely do I work on a family where the birth years and ages are totally and completely consistent from census to census. Sometimes the people themselves were inaccurate or careless. Sometimes the census taker got information from neighbors rather than go down a long road at the end of the day. We all know people who can't keep their own personal family info straight.
There are no Guilford marriage bonds for either James Brown around the time mentioned, or Green Rowe. But please keep in mind that not all marriages before 1868 required bonds! In 1868 NC started requiring marriage licenses. Please see the "Vital Records" page on Guilford NCGenWeb (link below). I put a considerable amount of information there, so I don't want to repeat it here.
You may need to check church and newspaper records. Try the Greensborough Patriot abstracts that are in the NCGenWeb Archives for Guilford (linked to the main page). Also, remember that people make assumptions (good and bad) based on indirect information, such as the names for wives or daughters in wills, land records, etc., and often forget to record or share the source for that assumption. Or "they found it on the internet." Also, someone may have assumed the marriage was in Guilford when it may have taken place in a nearby county. Generally, a couple marries in the bride's home county.
And -- last but unfortunately not least -- people make big, bad mistakes and post them all over the internet. Don't rely on someone else's info. Ask them for sources and then verify every bit of it whether or not they give you the sources. I've seen people cite sources that simply don't exist when I go looking for those sources. Either they were extremely sloppy (not good in more ways than one), or they simply made them up when asked for them.
Katherine Benbow
County Coordinator, Guilford NCGenWeb
http://www.ncgenweb.us/guilford/