Other particularly inspirational levels from the originals:

Taxing 6 "Compression Method 1" -- I mean partly the compression method itself, which often appears as part of a more complex solution, but more the fact that this was one of the purest examples of an "aha" moment where you are completely stumped, and then you have one insight and everything makes sense -- which designers often strive for and don't always achieve!

Mayhem 20 "No added colours or lemmings" -- The stand-out example of a pure puzzle level that has only one solution (except, apparently, in NeoLemmix, but even there, it took years for any skill saves to be found!)

Genesis Sunsoft 29 "I am A. T." -- the original digger staircase level is another one with imitations, variations and sequels in many packs.

From custom levels:

Lemmings Plus I, Psycho 28 "To the End!" -- the level that gives you 20 of everything except builders, forcing you to use several tricks to turn around and gain height so as to get around gaps that can't be crossed without builders.

MazuLems Level 9 "Holy Cow!" -- the originator (as far as I know) of the now-standard trick of placing bridges between two obstacles so a single basher or miner can keep going and cut through both of them. The trick is also pretty well hidden on this level, so it's not immediately obvious that this is the trick used even if you have seen it before!

I'm not sure how much I believe in this project, but if it's going to be done, it's worth making sure it gets done well so I could help with task B if you can give us the groups from task A as a starting point.

As a backroute method, DD itself is not actually all that useful in a lot of cases. The table in the OP of Lemmings (1991) levels that can be completed using DD shows that only a small handful of these solutions are actually backroutes: in most cases, the level is open-ended enough that using the DD solution isn't really a backroute, as such, and is more often than not far more diffcult to achieve than the regular straightforward solution.

This is obviously not a good test, since original Lemmings has a majority of open-ended levels where backroutes (of any type) are not really an issue. Whether you like it or not, a majority of forum members do care about puzzle levels and avoiding backroutes that trivialise the puzzle.

A better test would be to transfer a usermade pack made in a non-DD environment to a DD environment and see how many backroutes open up -- and ideally do this for several packs, since results for a single pack might be skewed by aspects of the individual author's design style.

Or, you know, you could assume that those of us with 20 years' experience of building levels in DD environments know what we're talking about

Yes please!

or 10 levels (1 tribe) for 12 people

Eleven. Classic has been done years ago and should be findable with a forum search.

What does Fiat Lem mean in English? Google translate doesn't have an answer... Or maybe it's just a reference to the car company I guess?

Fiat is the subjunctive form of the verb "to be", so it would mean "Let there be Lemmings!"

And whilst we're on the subject, here's a new trick for you - since lem recolouring for athletes is kept active in Classic Mode, assign a Floater or some other permaskill to one of the lemmings in a group, and this lemming will now visually stand out from the crowd! From there, it's very easy to see which direction that lemming is facing in, and whereabouts they are!

Does SLX prioritise assignment to floater-walkers over plain walkers?