Solution found (Thanks to Eddie at Technics) - it is simply that normal LOAD operations will load previous model data files (such as KN-6000) but Load Page 3 will not load previous models. When I saved ALL my files (that I had copied to SD from floppy) as KN-7000, then any Load Page 3 worked.

I had mistakenly thought that Copy from Floppy to SD would automatically change the files to KN-7000 files, but this was not the case. Load-then-save each file, solved the problem

Jim