I don't understand why Find My Past make such a big deal of opening redacted records.
In its simplest form, all they need is a 1 byte field on each record set to 0-closed, or 1-open, then, once a week or so, they run a program that reads every record, checks the DOB for 100 years and 1 day, and if it is set to 0, re-set it to 1, and copy details of each record opened to a file for later checking.
I have a database on my PC of over 5 million records, and such a program takes about 40 seconds to run, so it should take only 5 minutes or so for the 1939 database.
I appreciate that it is far from being as simple as that, as Find My Past state that new software had to be written, and that there is no comparison between the complexity of my records and those of the 1939 database, but the principle remains the same.