2 21, "You can't play with broken Lems": Totally not intended, but you still needed all the skills except one stacker, so it's a viable alternative solution to me. Also, it's not really obvious. I think solutions like these really require prior knowledge of how everything works, and I don't want to punish that. I went to quite some lengths to enforce the use of the main trick on Noisemaker 38, because it was required again later. But here, this level is the only one in the entire pack that even contains anti-splat pads, so I don't see it as necessary to enforce one specific solution just to make the player aware of how these objects work.
2 22, "Firework": intended.2 23, "Fields of gold": open-ended and fine as it is.
2 24, "Wonderwall": intended. The additional Basher is just provided in case the bouncing-it-off-the-Blocker part doesn't quite work. Otherwise the level would have been too hard for this position, at least for my taste.
2 25, "Radioactive": intended, as said above. In Old Formats, the radiation object is right beneath the receiver, and the pickup skill is a Blocker rather than a Bomber - that's pretty much all the difference. The fire traps were added in New Formats, though, to enforce Stacker usage, rather than allowing the Climber to go straight up the steel piece. In the Old-Formats version with radiation, the fire traps aren't needed, because the Stackers need to go in front of the radiation object anyway to prevent the crowd from walking into it.
2 26, "Like ice in the sunshine": intended. This one isn't really harder to execute in Old-Formats, though, because the slowfreeze is placed in such a way that the cloned Glider automatically stones in the correct two positions. Also, it's an 8-of-everything level in Old-Formats; hence, the extension to 10 skills was required in New Formats, so that I could provide additional Stoner pickup skills.
2 27, "Don't fear the Reaper": intended. Compression method is the way to go here.
2, 28, "Zombie": I've come to notice that timing-based solutions to Zombie levels are usually an option, and since this is the introductory level for Zombies, I don't see a justification for me to say that it's "forbidden". It's just usually a form of self-imposed execution difficulty, because it relies on the Zombie being in the correct position when the lemmings arrive at the exit. The cloned Stacker at the beginning is part of the intended solution, though. Any player who uses your solution actually demonstrates transfer of knowledge of the compression method taught on the previous level!
2 29, "Seven Nation Army": This level provides way more skills than necessary, just to make the skillset look "pretty" (descending from 7 to 1). It's pretty much open ended. However, I was impressed by how you used the Blocker on the staircase - the one that caused the Builder to turn around - to at the same time trap a lemming on the other side of that staircase, due to the trigger areas still touching the ground!
I might actually make that part of the intended solution on some new levels I create!
2 30, "Georgia on my mind": Once again a timing-based solution - in this case one that requires flow control, rather than compression method. There is the possibility to trap the crowd on this level, but since I generally consider flow control the more "advanced" approach, once again, I don't want to punish players who approach levels in this manner. Just like you suggested once with regards to Builder gaps - that advanced players who stretch out their Builder staircases out of a learned habit for skill efficiency shouldn't be penalised for their increased knowledge.
2 32, "Ich und mein Holz": Almost intended - you only spared the Bomber. The intended solution connects the block of one-way arrows with the crowd on the left via a Builder, then has the Miner carry on over the staircase. This requires the Basher to go beneath the crowd on the left, and then the Basher must be bombed to be stopped, thus opening a passage to the exit below. The way to enforce this intended solution to full extent would be to also put one-way down arrows on the wall containing the crowd on the left (which you bashed through). This would only allow a Miner to be used there. But your solution is so close to the intended one that I think I'm just going to leave this level as it is - it might even be a bit too hard for the second rank otherwise. Another case where I'm happy somebody found a slightly easier solution, compared to the intended one - that way I can feel like less of a douche!
2 33, "Eagle": Even though it took a lot fewer skills than required, this also looked much more elegant than the intended solution!
I think the only way to prevent this slight shortcut is obcessive amounts of steel, or horribly out-of-place fire traps (which have historically been my most frequent emergency responses to Builder-based shortcuts). Since however this is one of the "landscape" levels, and the backroute is not severe enough to warrant that, this level is also going to remain as it is, at least for the time being.
2 34, "Levels": Intended. Well, open-ended, of course; but you needed all the Builders, that's the intended part.
2 35, "Black Polished Chrome": Intended + Talisman (you saved the Climber from going over the stack). There are various ways to do this; the non-talisman solution bombs that Climber before he can walk off the screen and die. Arty took a completely different approach to this level; you however platformed over the market square, which is what I had in mind originally.
2 36, "Walk this way": Intended. Or, more accurately, the same solution Arty found, which is as close as possible to the intended solution. I originally wanted the pioneer to make another round, come back from the other side, then climb on top of the Stack blocking the exit, so that you can bomb it open. That's of course still possible, but overall, this solution is much cleaner and more appropriate for this position in the rank, while still requiring all the main tricks (turning around the Glider correctly and making the Fencer continue over the staircase).
2 37, "Shipping up to Boston": Intended. Though I do think you've also managed to spare one Bomber here.
2 38, "The Shocker": This level is also open ended, and pretty much just an exercise of various ways to get through semi-thin walls.
2 39, "Japan": I was very curious for this one, because obviously, this solution changed completely, compared to the original one including radiation. The original level is so complex that I didn't even attempt to replicate the solution here, but made up something completely different.
I didn't know that the masts with the one-way left arrows were thin enough to get through it with a Digger! This is enabled by the steel stopping the Digger; however, at the same time, the steel needs to be in this position to prevent the player from simply shortcutting by going beneath everything with a single Basher.
In the end, you still needed all but 1 skill, so I'm more than happy with this! 
I could enforce the Bomber usage at the masts by replacing the one-way left arrows with one-way down arrows, because these are the spots in which the lemmings need to bomb in the Old-Formats version using radiation. But I don't think I have to, given that, as stated before, the "intended" solution for the New-Formats version is completely different from the Old-Formats solution anyway.
2 40, "God gave Rock 'n Roll to you": Pretty much intended. This is really just a level to show off the Instruments tileset. The important things are the way the crowd is contained, plus the pioneer going along the top path in the beginning and then coming back along the bottom.
