Genealogical research many times is more about establishing a relationship between two people than it is determining a date precisely. Connecting a parent to a child is usually more important than proving someone was born on the 15th or the 16th of January of 1823. Knowing a date of birth to the month is usually sufficient. It's connecting a husband to a wife or a mother to a daughter that is usually key and where we don't have wiggle room like we do with dates.
In genealogy, it's often about the relationship more than it is the date.