OBD-II does not inherently record mileage. It does, however, greatly simplify diagnosing problems.
All I;m saying is the less electronics, IMNSHO, the better. Backfitting something to track mileage on an older vehicle is going to be interesting. Much like catalytic convertors and trying to enforce the law in 50 states. Since there’s no emissions testing in this state, mechanics DGAS.
A standalone electronics unit added to an older car can be beat.