Is that likely a different ROM, or just some kind of batch code used when the chips are made?
MP0271 is the ROM ID, so they are identical. I think NL indicates plastic package and standard temperature range, but I'm not sure what the 2nd L is for. I'm not sure about the "MSL" code. There are many other codes, but MSL is the most common that I've seen.
On Monkey See, the part of the case where the red and green LEDs are located is clear plastic with a sticker, almost like they were going to include a numeric display.