I just looked up the codes for Genesis Lemmings 2 on Gamefaqs and it looks like they are simply a password to unlock all 10 levels of a tribe, for each of the 12 tribes. A0;So there is no save in terms of your performance on individual levels.
But note this: A0;a password on that version is 22 letters long! A0;Even if we assume for ease of programming that each letter is only 16 possibilities, you still end up with more than 3*10^22 (3 with 22 trailing zeros) combos! A0;In contrast, with 60 lemmings and 10 levels, even a naive bound of 61^10 is only about 7*10^17 (7 with 17 trailing zeros). A0;(The bound is just combo of 10 numbers from 0 to 60, which is a gross overestimate because most combos will add up to more than 60.) A0;This means a random guess would only hit a valid password roughly 1 out 50000 times. A0;In short, even though the Genesis doesn't seem to support it, it is probably quite possible to come up with a simple-to-compute (for the computer) and "secure" password system that would serve as a save for your performance on a particular tribe.