One of the most useful pieces of information on the 1939 Register is the date of birth, since there are no other country-wide records containing birth dates other than civil registration records. Finding a birth date on the Register has solved a brick wall I had for one of my great grandfathers with a very common name; without this information I was unable to determine which birth certificate was the correct one.
But, how accurate is the date of birth field on the 1939 Register? I am not talking about FindMyPast's transcription accuracy – which does leave something to be desired. Rather, has anyone systematically assessed how accurate is the original data?
I understand that no evidence of date of birth was required when householders filled in the National Registration schedule. In browsing the records I have come across a few records with incorrect birth year or birth days. However, given that the Register was later used as the basis for NHS registers, I would hope that errors in the data would be reasonably small.
I think it is important to assess the data accuracy because a lot of birth dates on family trees will be drawn from this dataset – it is a much cheaper alternative to obtaining a birth certificate. If 1% of birth dates are incorrect, that may be acceptable, but if 20% are incorrect then we may need to treat this birth date data with extreme caution.