It's ridiculous that you cannot open the previous version of a Pages file in the current version of Pages! What an absolute joke.
Did OP delete those old versions? I don't see what the problem is here.
He got a new machine.
I would not mind buying a floppy drive and all necessary adapters, install Atari ST emulator and write Kamenicky encoding converter in Python to convert 1st World Plus documents from '89 if I had to convert documents of my parents. I would not be complaining about obsolescence of the format at all.
My problem is not technical, it is about user experience and productivity.