The pedant in me has to report your regex is buggy!
More specifically: the 1970 iteration will match lines like:
DOB 05-24-1952; SSN 123-74-1970; etc
I'm not sure if they exist but having had experience with cleaning messy data I worry. No, this is not likely to change your results meaningfully but it's the point of the thing. (Also, is each person's record written on a single long line? If not, you have a second problem!)
Doing this in fully generality is difficult but what I'd probably try is something like (not really tested):
cat file.txt | grep DOB | sed -e 's/.*DOB\([^;]*\);.*/\1/'
to extract all the DOB strings, then pipe the result to [grep -v '^....$'] to find anything not matching just a year, and build another sed expression to canonicalize each such class of lines until all lines are just a year.
AFAIK it's never made it into the legislature, but far right defence larpers love suggesting letters of Marque against China.
https://www.usni.org/magazines/proceedings/2020/april/unleash-privateers#:~:text=What%20are%20Letters%20of%20Marque,capture%20or%20destroy%20enemy%20ships.
https://warontherocks.com/2021/02/unfurl-the-banner-privateers-and-commerce-raiding-of-chinas-merchant-fleet-in-developing-markets/
The pedant in me has to report your regex is buggy!
More specifically: the 1970 iteration will match lines like:
DOB 05-24-1952; SSN 123-74-1970; etc
I'm not sure if they exist but having had experience with cleaning messy data I worry. No, this is not likely to change your results meaningfully but it's the point of the thing. (Also, is each person's record written on a single long line? If not, you have a second problem!)
Doing this in fully generality is difficult but what I'd probably try is something like (not really tested):
cat file.txt | grep DOB | sed -e 's/.*DOB\([^;]*\);.*/\1/'
to extract all the DOB strings, then pipe the result to [grep -v '^....$'] to find anything not matching just a year, and build another sed expression to canonicalize each such class of lines until all lines are just a year.
Normalization is really hard!