Hi Mark, why is it important?
The 1812 date on FAG will be a calculation by a researcher, mostly likely based on one of the surviving census records:

Unfortunately the US federal census takers are notoriously bad at records of age, but in this case the very tight scatter suggests a DOB of either 1811 or 1812. But the problem is the 1860 and 1870 records are both made 10th Aug and being exactly 10 years apart the age recorded should be X and X+10 but it is not so there will always be an uncertainty.