Hm, this one uses Lemmings (U) (V1.0).smc, while I used Lemmings (U) (V1.1) [!].smc ... not sure what's different between them if anything, but the timing is a few frames off (desync) if I use the wrong ROM ...
Anyway, comparing with
my run now:
(end of each level, when it fades out completely)
lvl -- mine - yours ---- diff
01 -- 2563 - 2536 --> +27 (gain: +27)
Small gain from digging the minimum height, while I was 1 pixel too high.
02 -- 4357 - 4324 --> +33 (gain: +6)
03 -- 6384 - 6461 --> -77 (gain: -110)
Setting the 99 drop and first blocker was too slow.
04 -- 9429 - 9663 --> -234 (gain: -161)
Bad timing for when the mining ended, all the other lemmings had to walk back and forth the whole way before falling.
05 -- 12566 - 12783 --> -217 (gain: +17)
06 -- 14642 - 14947 --> -205 (gain: +12)
07 -- 19032 - 19071 --> -39 (gain: +166)
Good improvement there, yet it does look like it could be even better, with the 2 lemmings you missed ...
08 -- 21454 - 21494 --> -40 (gain : -1)
09 -- 24219 - 24208 --> +11 (gain: -51)
All the messing around in my run must have cost more time than I thought here ...
10 -- 25568 - 25641 --> -73 (gain: -84)
Slow start again.
11 -- 29677 - 30003 --> -326 (gain: -253)
Faster digging from the right (using multiple lemmings) but you didn't go all the way with it, which must be how you lost 4 seconds ... I used the spare bashers on the left side instead, but I'm not sure which one is faster.
12 -- 33112 - 33058 --> +54 (gain: +380)
Possibly more lag by not killing off the last lemmings, but using bombers to clear the way at the end was apparently much faster (and smarter) than builders.
13 -- xxxxx - 36942
Mine stopped there so I can't compare, but I'm sure you were a little faster there as well, by setting the diggers in a way the last lemmings can simply walk down (I made all of them dig).
Overall, this is hardly an improvement on mine yet, although some parts were definitely better ... also remember you can hold B to move the cursor faster, which really helps sometimes.
I'm working on my own improvement now as well to see if I could do better, and redid the first 3 levels so far:
http://acmlm.cjb.net:2/emu/snes/snes9x/smv1/Lemmings-b1.smv
Comparing this new one with yours:
01 -- 2536 - 2398 --> +138 (gain: +138)
A new trick I found: 10 lemmings together dig faster than one!
02 -- 4324 - 4187 --> +137 (gain: -1)
03 -- 6461 - 6115 --> +346 (gain: +209)
The drop rate and first blocker were optimized better.
Finding the optimal drop timing for level 4 won't be easy ...