Anything that does not record a contemporaneous event is questionable in my opinion. If a birth is recorded within a few days of the event it's most likely accurate, if it's from a census, seigniorial register, marriage, or death record it's an educated guess at best. I have found church books with the scribe scribbling the year minus the supposed age at death in the margin to come up with a birth year - and forgetting to carry the one particularly when the times cross a century marker - starting with a guessed age and then missing a decade because of faulty math.