I've often wondered about best practice with this.
If I know the date of a birth event, obviously I have an actual date to record against it.
If I don't have an exact date but do have an approximate year (say from an age given on a census) I can put something like c.1865.
But then what do you put if you have just the name of a Father on an old marriage registration? The son could be one of up to 14 children (I have ancestor families that big) and if none of the other siblings is known, any approximation of the fathers year of birth would be very wide of the mark, even if you assume he was married at age 21.
Hello
If you have a Place of Birth (from the Census), a Father from the Marriage Certificate and an Age from their Death Certificate (or even an approximate Birth Year in the Census), 90% of the time you are halfway there in trying to get the correct Birth or Baptism image of the record, unless it is a very common surname, and in London or other big City.
If you have been getting Death Certificates going backward as well (as the Marriage Certificates you have been getting and Birth Certificates), I would hope that you would get the first Birth or Baptism prior to Civil Registration in 1837 and hopefully get back a bit further still?
Working out when someone dies, checking the Death Certificate details look right and working out where they are buried to see if they have a Memorial stone (a few photos are becoming available online now) and what their Memorial says was just as important to me.
However, it very much depends on how far you want to go back, what kind of budget and time you have available I suppose, as to whether you try and find their actual Baptism or Birth, rather than put an about Birth year and stop there?
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In 1999 I had got back to a place and I had found him in the 1841 Census, got his 1845 Death Certificate saying he was 60 years old.
Twenty five years on, I have collected a massive amount of related documentary material, Wills, his Burial record held in a University Special Collections (not online), some information from newspapers and some held in Archives (some Deed Packs are still with a Solicitor whose client owns the building upon which my ancestor's buildings once stood), plus other information about him and my wider family by marriage, but never been able to confirm his parentage and my Line before circa 1785!
Mark