As I promised, here’s the flimsy explanation for the rear window.
Everything’s possible with a little fantasy. I had already drawn this picture and filled in the text, when in came to my attention that this was in fact the key to my little ‘problem’.
And in fact, you have to show me some good proof why it shouldn’t be possible for a skilled mechanic to fix this car together with bits and pieces of several other Beetles.
I wouldn’t have needed this ‘explanation’ in order to relax. But since it came along so easily, I take it as a good excuse.