There are things that researchers will not be able to pinpoint precisely. No record might exist that provides great-grandfather's exact date of birth--and March of 1874 may be as specific as you are going to get.
Keep perspective though. Bigger concerns are that you have this ancestor tied to the right parents, sibling, spouse, children, etc. A date of birth that is not specific is not always the end of the genealogy world.
Sponsored By GenealogyBank
