I was thinking a little bit different way - for example:
[R14 XDG Updates] Updated=R14.0.0
or (maybe better - can cover also changes during development versions and also easier for comparison in shell)
[R14 XDG Updates] Updated=20130407
Where timestamp is not date of the conversion for user, but the internal date of r14-xdg-update script, which make conversion.
Makes sense. Or use the time stamp of tdelibs/tdecore/tdeversion.h or TDE_VERSION_STRING from tdeversion.h
Darrell