Hi Kieran,
I have solved all of the levels in this small collection. My replays are attached.
General FeedbackAs stated in the OP, Kieran started work on another level pack while being on and off about the QFK pack. Until now, these levels have never been seen by anyone other than Kieran. Honestly, in my experiences I found a lot of these just as hard as the levels in his QFK pack, though I admit some of these I was a really big dumb dumb.
For example, NGL, I was actually stuck on the first level for a good half hour or so, and I even thought it was impossible and was wondering how in the world is it possible, after I have officially ran Kieran's official solution for the level through the MRC and it reported as "passed." Turns out I was very dumb and overlooked one critical thing (more details later). Even then, it was also nice to see some of the levels which likely won't ever be put into an official level pack.
Abandoned Rank FeedbackAs I recently finished my LP of QFK, I thought I take a look at these rejected levels that were slated for the next level pack that Kieran was making, especially since it's just 10 levels and hence I thought it wouldn't take too long. Turns out to be very wrong, as there were three levels in here that took me quite a while before I solved it. These were Abandoned 1, Abandoned 4, and Abandoned 6. Abandoned 10 also took a while only because of the solution being very precise even though I've realized it very quickly. It probably wasn't a very good idea that I went through this small collection pretty late at night, when I wasn't really at my sharpest

Abandoned 1 -
Letting You Down Gently As previously mentioned, I was a huge dumb dumb on this level and eventually thought how in the world is this possible after I ran your solution through the MRC, until I finally realized the key thing I was missing

In actuality, it's a very easy level indeed.
The thing I was very confused about is how in the world can they get to the exit if you have to platform to the left and then fence up to the crowd, as because the platformer seals off the gap completely there's no way out. Then, after a very long time, I realized that the floater is supposed to go through the top and float down to the bottom again after that so that he can fence away the platformer bridge and hence allow them to reach the exit. Ugh, I can't believe that went over my head.
Abandoned 2 -
Low Tide Not much to say here other than my solution is probably a bit more complicated than the intended one. This one still isn't easy to figure out despite it just being a 2-lemming level.
Abandoned 3 -
Stepping Stones Another easy one, and even the talisman solution isn't that much harder

Abandoned 4 -
Abseiling Another one I was a huge dumb dumb on, though at the same time it is a hard level, and there's some red herrings here that look like they could work but don't. Nice solution, though!
For some reason, it took me a while to realize that I could platform from both sides with the first gap at the top, where one goes to the right and then another goes to the left a level lower. This would allow the crowd a way out and be able to get down.
Before I found a working solution, I thought to use the dart to bash and then platform and stack to release the crowd with bashing, but turns out you'll be a platformer short this way. Nice!

Abandoned 5 -
Tartan Stack Nice medium difficulty level here, though the timing here can be a bit tight, especially as the main challenge is due to how you can only lose 1 after using all cloners.
Abandoned 6 -
Climbing the Castle One of the hardest levels in this collection, though I overcomplicated the solution with some very precise skill assignments and timing.
I've learned something new here with the bombing to stop a miner so that he can go the other way and it'll still be possible to platform up the gap and step up. Normally, you would need to interrupt midstroke to be able to platform.
Nice to see that the falling from above to bomb the stack away to release the crowd is intended!

Abandoned 7 -
Roofer Madness Nice fun one to figure out. The talisman solution is somewhat challenging, but it luckily isn't too difficult.
Abandoned 8 -
Sink Holes Yea, seems quite backroutable

Abandoned 9 -
Final Resting Place Backrouted as well, and I've seen the intended solution which is definitely far more impressive than my solution.
Abandoned 10 -
The Ultimate Quest, Take 5 Yea, this one is somewhat harder due to the precision needed, though I pretty much had the solution figured out after about 5 mins or so.
I actually tried doing the building in a way so that the climber doesn't turn back but I couldn't get it to work. After watching your solution, turns out that it's very precise and seems that you cannot stretch the bridges at all, which was why it didn't work. I eventually abandoned this and found a very precise digger placement to stop the climber from going back out to the left. The rest of my solution is pretty much the same except I built over the exit and used the steel to bash and make a hole to stop the climber going out the wrong way.
Overall, these levels were still somewhat an enjoyable challenge, even with some still in a backroutable state. Thanks for releasing these!