Hello Icho,
I have solved the new levels and also resolved all levels where my replays broke. I have my entire replay collection attached.
Regarding the new levels:
3 22 -
The Graveyard Wow, this was an unusually tough one for me but it's a great one. Demonstrates the three tricks needed to avoid further zombie infection well.
I was a dummy and simply didn't think of having a lemming turn around on a blocker before assigning him a blocker and hence why I kept losing more than one lemming or needed to use two walkers, one to release the blocker and another to turn him around unnecessarily
3 23 -
Laboratory of Explosions Easier than the previous level, but it definitely helps that I'm already aware of both of these tricks mentioned in the pretext. Even then, they occasionally go over my head!

Still, that's great that a level that teaches this is made for the NL Tutorial pack

Interestingly enough, I beat this level without the pretext ever loading, but that's because I have discovered a bug and I'm able to reproduce it.
3 24 -
Containment Breach Yet another level that I was able to mostly figure out without the pretext ever loading, although what was mentioned in the pretext for this level I had figured out on my own. Once again, I was a dummy and completely missed what I mentioned in the spoiler for 3 22 above and therefore I was short a skill

It's amazing how sometimes these things get overlooked

6 8 -
Saving Two Lems with One Bomb O.o, this was my favorite new level!

Not only is Proxima's tileset really nice, I really love the puzzle here. I remember namida suggesting on Discord this trick be taught in this pack.
6 9 -
Stack and Step This was an unusually difficult level for me, and that's because I found it quite odd that the pre-text never even loaded when I first played this level. Even then, while I was trying to figure out what tricks you intended to teach in this level, I still managed to solve it on my own

I have mentioned in various places around here that levels that provide lots of stackers tend to be hard ones for me. You can pretty much say these are "hard for kaywhyn levels."

Even then, this should be a backroute, considering I don't even use one of the tricks mentioned in the pretext when I did find out later on what it said.
6 10 -
Jump the Sausage! This was also a difficult level for me, but it's a nice one. I'm glad that you put these levels teaching some stacker tricks, especially since they can be some of the most difficult ones to do. Even then, that didn't stop me from being able to complete certain United levels that required these tricks

This might be a good time to add some tricks to Strato's topic on the stacker skill:
https://www.lemmingsforums.net/index.php?topic=3864.0Levels I needed to resolve: 6 4 -
Walking Over Dead Bodies6 7 -
Checkerboard's Crossing Much easier now than it was before thanks to all the pickups.
6 12 -
Shimmichanga Now the walker is relevant instead of optional.
6 17 -
A Different Kind of Space