Given how you have 99 of everything, it's definitely possible to save every lemming in Hellish 20. As a matter of fact, because the most difficult part is at the very end and how there's so many nasty surprises that you can't even see, it was suggested to Arty that he tone down the level by drastically reducing the save requirement. Regarding Retro 20, I think that level is broken now, because I tried it sometime a few weeks ago, and it doesn't seem like the level is solvable anymore. Probably because of the new Superlemmini versions earlier this year that maybe makes the glitch not work anymore. When I played the pack back in the day, it was possible, but now it doesn't seem like it is.