All of the modeling I have done, or seen done, has always
been on virgin devices. I have yet to encounter a model
set which includes aging, even as a corner. Rather, the
norm has been to constrain allowable drifts in qualification
and make the process guys hold up their end if qual fails.
But I gather this is not the norm in commercial sacrifice-
anything-but-the-pennies-per-part product development,
DSM foundries would rather it be your problem than theirs.
So good luck with that.