Finally! I have just effectively completed all of GameBoy Lemmings. "Effectively", because I got lazy on Mayhem and only played the levels where you are not required to save 100% in order to pass, obviously because for the challenge purposes here, you don't really care about 100%-required levels. Besides, they probably play more or less the same way as their NES counterparts which I did play through.
(On GameBoy Lemmings, the non-100%-required Mayhem levels are: 1,2,3,4,13,15,17,18,19,20,23,25.)
And so, my current records for all of GameBoy Lemmings:
Fun 3: lose 5
Fun 6: lose 2
Fun 23: lose 1
Tricky 1: lose 1
Tricky 3: lose 1
Tricky 6: lose 2
Tricky 13: lose 2
Tricky 17: lose 1
Tricky 18: lose 1
Tricky 19: lose 12
Tricky 25: lose 1
Taxing 7: lose 1
Taxing 10: lose 1
Taxing 11: lose 4
Taxing 20: lose 1
Taxing 21: lose 2
Mayhem 2: lose 1
Mayhem 13: lose 1
Mayhem 15: lose 3
Mayhem 18: lose 1
Mayhem 20: lose 1
Mayhem 25: lose 2
Total lost = 47
So I did 3 better on the GameBoy compared with the NES, and most of the better (and different) scores come from Mayhem levels. A brief explanation of the differences:
Mayhem 1 (100% on GB, lose 1 on NES): Because on the GB unlike the NES, builders can turn themselves when they hit a wall while in mid-build, the level can be passed with only 16 rather than 17 builders. This give you one more builder to deal with crowd control. Also help are the facts that: 1) GB walker's speed (relative to builder) is slower; 2) you can switch skills while the game is paused unlike the NES.
Mayhem 3 (100% on GB, lose 1 on NES): The digger and basher's effect is more incremental on the GB, more similar to the regular versions of Lemmings. So for example, on the GB and unlike the NES, making the first lemming out dig will divert all but one lemming to the next lower platform. Hence the 100% GB solution cannot be done on the NES.
Mayhem 13 (lose 1 on GB, lose 2 on NES): On the GB version of the level you are given 1 more basher and even a miner, plus some of the terrain which are not bashable on the NES are bashable on the GB.
Mayhem 20 (lose 1 on GB, 100% on NES): The main reason 100% proves impossible on the GB is its limitation that only 3 terrain-changing skills (builder, basher, miner, digger) can be active at the same time. So for example, you can't get enough builders going to stall on both sides of the platform, despite the slower walker speed on the GB. There will also be issues with freeing the blocker if you try that idea, because of game mechanical differences between the GB and NES.