XDPX Version Confusion with Open Files

[Boy]

I have eight files open in XDPX16.2: 3 x Unsaved; 3 x Saved but Modified: 2 Saved.
For some reason these same files open in XDPXv11.5.2, all complaining there have been created in a newer version.
This is not happening with XDPXv12 or XDPXv15.

I'm not sure if I fully understand what you're saying but when I open files in XDP 15.1 that were made in a later version, I do get the warning that they were created in a newer version.