One of the resources I rely on often in my research is the Census. It is in a way both very reliable and yet very unreliable at the same time. It does tell us who was living in the house at that time, usually indicating with some degree of accuracy what their relation was to the head of the household. Ages are often wrong. I expect it's because the person giving the information didn't know the actual birthdate of each person and just gave their best guess. Like "oh .... I'd say about 9" ... not remembering that 10 years ago at the previous census the child had been recorded as being 2.
Some census years are better than others in the areas I've been focusing on, and I imagine it's the same everywhere else. The census taker probably didn't lay eyes on everyone he was listing, so he may not have noticed that someone was older or younger than recorded, or if it should be listed as Male or Female. Some often put down the nickname of a person rather than their actual formal name. So little "Gussie" listed as being a 9 year old boy may have actually been Augusta, an 11 year old girl.
Spelling varies greatly from one census to another ... if a person lived long enough to span several censuses you could see a whole slew of different spellings.
I can't be too hard on them though, seeing as many had little to no actual schooling and were doing the best that they could with what they had. I guess I should be grateful that I haven't come across a census with "One-eyed Willie" listed in it.
