Easiest way for a program to get the datestamp on a save file's contents?

["James H. H. Lampert" <jamesl@xxxxxxxxxxxxxxxxx>]

Not the "created" or "changed" or even "last used" date stamp, but the 
date when the save contained therein was done.

I'm working on a bug in a program that automatically updates a save 
file, but ONLY if it's out of date.

I'm currently using the "changed" date, and just discovered that if I 
restore the save file from out of another save file (to reset back to 
the original conditions), the "changed" date doesn't go back to what it 
was, but remains at "today."

--
JHHL