Actually with each shelf release the 2d Clients differ. For instance... 8th Age client has a different way of storing character information on the HDD than the ML release. There are various changes with each 'pressing' of the CD. Its not just patching etc etc. If you look at your patching downloads it'll actually have what pressing it is.. SE, ML, AOS, LBR etc etc.

The old old clients will do things differently than the newer ones