Indeed, this was *not* written to check the chip, just the assembled product (the original full test was sanctioned by the safety-at-work inspector - the operator would fall asleep & fall off his chair! 8-)
Inspired by the "check address lines" phrase : has anyone ever swapped around the address lines &/or the data lines, either by design or by accident (manual routing)? In theory, it should make no difference (Eprom is another kettle of fish!).

Regards,

Richard