> SUP Requesting changes since Dec 31 16:00:00 1969

Ah.  You installed the latest sup, then.
At some point (quite some time back, actually) the format of the timestamp
files was changed from a raw four-byte integer to a character string (which
is the number that was previously written out in binary).

The simple way to recover is to use "od -l" to find out what value is stored
in the last.* files in /usr/sup and then echo the corresponding value into
the files.