Placeholder dates for date of birth in GP data

[spiros]

UK Biobank uses placeholder dates for GP events where the date matches the participants date of birth. Specifically,

• Where the date matches participant date of birth it has been changed to 02/02/1902.
• Where the date follows participant date of birth but is in the year of their birth it has been changed to 03/03/1903

We can overwrite these dates in the data during ETL and set them to 01/07/YOB where YOB is taken from the baseline assessment data (recorded as data field 34.

[MaximMoinat]

Note: in the latest run (June 9th), there are no 1902/1903 dates. This run, only the covid19 gp data was taken as source for GP, so it seems like these placeholder dates only occur in the regular GP files.