I looked at some of the default shows that are contained inside the firmware files.
At least those shows are a compressed directory structure with a .tar.gz extension. They should be readable by *nix utilities; I used 7zip on Windows.
It appears that file formats may have changed from v1.8x to v1.9x. I don’t have any older files than 1.86.
If you can get inside the firmware file, look for the version.dat file. It appears that it contains a text code, and “11” appears to refer to the 1.80 file format, and “12” appears to refer to the 1.90 file format.
Be aware that some utilities might have the ability to modify-in-place so I recommend making a copy before messing around inside the file to make sure you don’t introduce any corruption.
Also consider the possibility that it is not a version mismatch issue, but that the file won’t open because it is corrupted.