"Files saved in V13 can be opened in V12 - presumably because the same basic structure was used for both versions."
Or because no new internal features were added in version 13, which would have required new data structures. *THE* reason for no backward compatibility is because new versions contain new features that didn't have any place to stored in the previous versions' .veg files' data structure.
Yup. 'cept the Windows Layout Keystrokes. They don't appear to have been cross-version compliant. I just got the: "You are using and older . . Layout . . blah blah".
Kind of related, over the weekend I found that if you use a Vegas with cinescore data in it, the 64-bit version reads that as a plain wav file. The 32-bit version of Vegas reads the cinescore data. So you can still edit the cinescore files after you modify the veg in 64-bit vegas.