I just tried MOV A,ACC on the Cygnal test board and it seems to work fine; i.e., it doesn't really do anything. The value of the Accumulator and all other registers seem to remain the same--except the PC which is incremented by two to point to the next instruction.

Have you actually tried the instruction on a Philips part? Despite what their documentation says I can't understand why it wouldn't work. Perhaps they just meant to say that it's a useless instruction. But even if the instruction "fails", what damage does it do? Failing to move the accumulator to the accumulator is the same as succeeding at doing so.

Can anyone with a Philips part test the MOV A,ACC instruction and see what happens?

In any case, regardless of whether or not it "works," why does it matter? Why is this of interest to you?

Craig Steiner