David,

Here is a post-facto but pretty pragmatic answer:

If you really care about clock accuracy, you are running NTPD.

If you are running NTPD, then the kernel's idea of the time *will* be
better than a PC CMOS clock ("dallas" RTC or moral equivalent, or the
Intersil(?) used in early Sparcs). So the kernel should write its
NTP-disciplined time back to the battery-backed up clock on shutdown.

Conversely, if you're not running NTP, and the kernel drifts, then
there is little damage from writing the kernel time back to the
battery-backed-up RTC chip -- since, as you're not running NTP, you
clearly aren't too fussed about the accuracy of your clock.

If we limit discussion to mid-90s workstations, or even PCs, then
there's a bunch which used RTC chips that were not at all
graceful about Y2k (or, in extreme circumstances, 1996.)