Most of the levels that seem similar have small differences. Here are all the game mechanical differences that I can think of now:
1) You can't change the RR instantly.
2) Pausing at the beginning doesn't change when the lemmings come out.
3) Both sides of the level act as walls.
4) A digger has two pixels on each side that don't support him.
5) There is no "right click to select only walkers" function.
6) The mayhem 12 glitch doesn't work.
7) OWWs are where they appear to be.
8) There can be up to 100 lemmings. (obviously only affects some levels)
9) A builder turns around when he hits his head on the top of the level, and I think it happens 1 or 2 pixels lower.
EDIT: This is compared to DOS, I don't know about the Amiga.
EDIT2: While I was playing through tricky 21 I made a lemming slide through some terrain again, but this time I got it to happen several times (thanks to savestates). So this time I observed exactly how the sliding lemming looked, and I figured out how to trigger it. It makes sense considering what I know about the game mechanics, and it seems so obvious now that I know what it is...
Leviathan, I can PM you about it if you want.
Right and
left sides of Trcicky 21.
Tricky 12Mayhem and Present:
Mayhem 2: 99/100
Mayhem 5: 76/80
Mayhem 14: 48/50
Mayhem 19: 47/50
Mayhem 29: 84/100
Present 2: 43/50
Present 16: 98/100