The tz zone description file zone1970.tab who replaces the old zone.tab file, is not present in fresh 12.1 installations even if the file is present in the svn repository (freebsd/contrib/tzdata/zone1970.tab).
Only the zone.tab file, who is required for compatibility purposes is currently available.
This table is intended as an aid for users, to help them select time zone data appropriate for their practical needs
This was fixed by tmunro@ in head in r350079 (2019-07-17 06:17:27 +0000) but never merged to stable/12 or stable/11.
Thomas: could you merge this changes to the stable branches please? Or would you like me to do it?
I will do that -- please give me a couple of days.