Really? What was the system?
Based on a skim of the code in an old commit that still had it (77ae002 is the one that removed it), you'd begin the level with 50,000 points, and your score would decrease based on certain things happening (but could never drop lower than 100 no matter what). Where one of the penalties implies another (eg. "level failed" also implies "didn't save 100%"), the lesser penalty still gets applied as well.
Level outcome- Failure to meet the save requirement: -10000
- Failure to save every lemming (including Cloners): -1500, and a futher -100 per lemming not saved
Time penalties- Prior to the first lemming being saved: -2 per frame
- On or after the frame where the first lemming gets counted as saved: -1 per frame
Skill usage - Each time a skill is used, the corresponding deduction is made.
- Walker: -10
- Climber: -25
- Swimmer: -35
- Floater: -20
- Glider: -55
- Mechanic: -40 (now known as "Disarmer")
- Bomber: -20 (plus the penalty for losing the lemming)
- Stoner: -15 (plus the penalty for losing the lemming)
- Blocker: -25
- Platformer: -90
- Builder: -120
- Stacker: -45
- Basher: -50
- Miner: -50
- Digger: -50
- Cloner: -200
- (The Fencer, let alone the Shimmier, Jumper, Slider and Laserer, didn't exist yet at the time scoring was removed)
Other- Triggering a trap: -150 each time
- Increasing the release rate: -100 the first time, no penalty after that
- Decreasing the release rate: -200 the first time, no penalty after that
The score was displayed on the postview screen, and high scores were saved. No one ever really paid much attention to it, so it got culled (technically as part of the major cull / tidyup between 1.43 and 1.47, although it got merged into stable versions a tad earlier, with the score first removed in 1.43-C).