Lemmings Plus I Medi 7 "Leap of Faith" (http://www.neolemmix.com/old/levelimg/lpi/0307.png)
The solution - in particular, the talisman solution, is set up to make use of direct drop. Could possibly be avoided by making the fall less high; in terms of simply solving the level (not the talisman) it would remain possible as the level provides enough floaters for 1 per required-to-save lemming. There are alternate, slightly-more-complex solutions that also avoid direct drop, but none of these would earn the talisman.
Lemmings Plus I Psycho 6 "The Bulldozer" (http://www.neolemmix.com/old/levelimg/lpi/0506.png)
The only workaround here would be to use antisplat pads on ground near the bottom, which the fire set does not currently have (of course, with NX2 planning to allow mixing-and-matching of graphic sets in a single level, this is not such a huge deal there); with an exit also on that platform. The most obvious thought to come to mind may be to simply pre-assign all lemmings Floaters (or provide 80 floaters in the skillset), but this would in fact open a major backroute.
Lemmings Plus II Genius 20 "Cactus Central" (http://www.neolemmix.com/old/levelimg/lpii/0520.png)
This level is intentionally designed to make use of direct drop, without being obvious that it exists. Even the above alternative might not work great here, as the whole point is to not draw attention to the feasibility of direct-drop. With that being said, most levels in LPII where direct drop poses a threat already have measures in place to avoid it (see Diet Control (http://www.neolemmix.com/old/levelimg/lpii/0504.png) for example).
Lemmings Plus III Timid 11 "A Digger Would Be Handy" (http://www.neolemmix.com/old/levelimg/lpiii/0111.png)
This one could be worked around by placing steel underneath the exit. The height of the window and exit would have to be adjusted so that the fall from the window to the newly-placed exit platform is not fatal (or alternatively, all lemmings pre-assigned floaters, which could confuse players into thinking that the floater, rather than the radiation fields, is the key to the solution; or use updrafts, which would mean introducing two new objects in a single level - although with that being said, this is less of an issue now that the NeoLemmix Introduction Pack exists for this purpose).
Lemmings Plus III Fierce 1 "Dead Is The New Black" (http://www.neolemmix.com/old/levelimg/lpiii/0401.png)
This is perhaps the strongest example. Although this level involves an ohnoer, not a faller, exiting; the overall nuance is the same - NOTHING other than allowing direct drop would leave this level solvable, especially because of the case being an ohnoer - unless someone can think of a reasonable argument as to why an ohnoer should be able to exit (whether on land or not), yet a faller and perhaps even a floater should not? The only real alternative is to replace the bomber with a blocker, but that in turn replaces the level's very unique trick with one that's rather commonplace.
Lemmings Plus III Fierce 5 "In The Frenz-zone" (http://www.neolemmix.com/old/levelimg/lpiii/0405.png)
Although this one doens't require it in any way, this is a very fast-paced and hectic level, where the player may not have the time or reflexes to ensure the bridge goes to the exit, rather than over it. In this case, allowing direct dropping into it removes one element of artifical difficulty. Granted, that's a bit hypocrital to focus on considering that this level probably has more artifical difficulty than the entire remainder of the Lemmings Plus series combined; but even so...
Lemmings Plus Omega Puzzling 3 "Horizontal Access" (http://www.neolemmix.com/old/levelimg/lpo/0203.png)
Similar to the above case, it avoids the need to accurately aim for the exit. The difference is that here, there's no pressure in terms of time as such, but rather the approach towards the exit is horizontal from all the way across the other side of the level (due to a lack of constructive skills other than platformers).
Lemmings Plus Omega Perplexing 20 "Current Affairs" (http://www.neolemmix.com/old/levelimg/lpo/0320.png)
This is another no-alternative case, except by discriminating between fallers and other actions in midair (in this case, gliders). Aside from the initial setup to get gliders for both lemmings, the main puzzle here comes from that you have no way to reach the exit apart from gliding into it, even though the level appears to offer alternatives at first glance.
Lemmings Plus Omega Mental 18 "...wait, what?" (http://www.neolemmix.com/old/levelimg/lpo/0418.png)
Due to the exit being upside down, the only really obvious way in is to drop in from above. The level's earlier clone provides enough skills that you could create a solid standing spot below the exit's trigger area, but this version (as far as I'm aware) leaves no other option.
Lemmings Plus Omega Mental 28 "The Troublesome Trio" (http://www.neolemmix.com/old/levelimg/lpo/0428.png)
This is one where it's not such a huge deal, because the exit could be moved. This would have some impact on disguising the solution, and may also require improved accuracy when aiming for it (but not to nearly the same difficulty of such as other levels with this problem), but should at least not open backroutes.