I’ve experienced similar annoyances with old scores not displaying the same in newer Cubase versions (though, TBH, it’s not been a big problem for me).
My “solution” is to keep the old versions of Cubase when I upgrade. Perhaps I’ll get stymied at some point when a version I used on an old PC won’t be able to be installed on a new PC with a different OS (and the old PC that had the working version of the old Cubase dies)?
I wonder whether it would be possible to install the old Cubase in a virtual machine (on a new PC with, hypothetically, an incompatible OS), just to open old scores - could Cubase see the dongle?
Another thing to do in circumstances when all you want is to be able to see/print the old score again, rather than edit it for a new/revised piece, might be to save the score as a pdf file, or even (rather quirky, perhaps) do a “print to file”, which (so long as you still have the same or a compatible printer) you could simply copy to the printer, to get the score printed again.
But, if you’re creating a new or edited piece in a newer version of Cubase, based on an old piece created in an older version of Cubase, I think you’ll probably have to rework the score if it doesn’t come up the same in the newer version of Cubase.
It’s disappointing that there isn’t backward compatibility.