By trying 2039 you hit the "Year 2038 problem"

Any system, including Macs, that use a 32 signed integer for time will stop counting time properly at exactly 03:14:07 UTC on 19 January 2038. Its a well known issue in time keeping for 32-bit systems.

As far as I'm aware, fixing this is much, much more difficult.

So, by fixing the 2020 issue, we have just delayed the inevitable for another 18 years.