Bruce! Do you have any idea why these "fake" pins?

Very useful! Will you put them on your web site along with the schematics so people can find them easily?

No I don't know why there are fake pins but it is very possible that 72 pins was just a standard size from the manufacturers. The contents of the chips was custom but I doubt whether the actual package and pinout shape was (although I can't actually remember!). It is also possible that one or more of the "spare" pins is an undocumented test pin, ie. something interesting to the designers (and no doubt you !) is output on them.