In an ancient message you said:

In message <199603230235.SAA03000@gabriella.resort.com>, John M Vinopal writes:
>On some netbsd machines I run, ps a gives all process dates as being
>31Dec69.  What precisely causes this?  Do the kernel, libkvm, and ps
>all have to come from the same compilation?
>On one machine I've recompiled and installed libkvm, then ps to no 
>effect.  Why does this seem to get so easily out of sync?

This happened to me recently.

31Dec69 would put it just before the epoch, so maybe it's a negative number
(0xFFFF....).  I had to re-install the include files and then recompile
to fix this.  Or maybe it was the fact that I booted of /netbsd.whatever
instead of /netbsd.
In any case, ps is reading the wrong thing, as you probably guessed.