My question (yes, sorry it took so long to get to it) is this: Would/Could changing a byte outside the bank's size result in an occasional, hard to reproduce, error that does not necessarily occur at the moment the byte is changed but at any, effectively random, point during the program's execution?
Can't say how it goes on all machines, but here I get an offset out of range if I make any attempt to write outside the bounds of a bank, so I'd have to say no.