This might sound like an odd question, but...
Were there 2 sizes of manual for the 464? Amongst my collection of four 464s, only one came with a manual which is pretty much A5 shaped. The 6128 manual I have is similarly size. However, my recollection of the 464 manual I had when I was younger was maybe not quite A4 sized, but certainly at least 2/3 A4 sized, so about 50% bigger than the manual I've got now. I fully expect they reduced the size of the manual to reduce costs around the time they went to the cheaper half-height keys, but that's just speculation.
I don't particularly want a bigger manual, I just want to know I'm not imagining this!
My 464 (spanish version, 1986) came with both versions of the user manual, and I have no idea why. The "bigger" one looked like a straight translation of the english manual, and the smaller one seemed to be more adapted to the spanish market. In fact it was almost the same as the 6128 manual.
Cool, thanks for the info... :)