I'm mainly worried about that chip, even though it has a sticker on it, it appears that it may be a mask ROM. I wouldn't suggest pulling the edge of the sticker up, but to HyperGHZ: if you run your finger across the center of the chip, does it feel like there is a UV window underneath? If it's a mask ROM, I'd be almost certain that it's a final version. If there's no window, that doesn't necessarily mean it's a mask ROM, however, since you say that there are differences. It could be a one-time PROM that is not erasable.