Levels which most likely intentionally have multiple solutions, for example Tricky 9 "They Just Keep On Coming", shouldn't be counted as backroutes. However, when the intention of multiple solutions is questionable, assume the worst.
I'm mostly only aware of backroutes in Lemmings 3D. Ask if you want to know the details of any of them.
Original LemmingsTricky 19 - Postcard From Lemmingland
Tricky 25 - Cascade
Tricky 30 - The Crankshaft
Taxing 4 - Lend A Helping Hand
Taxing 6 - Compression Method 1
Taxing 22 - Come On Over To My Place
Mayhem 24 - All Or Nothing (Versions with arrow key support only
)
Mayhem 29 - Save Me! (I heard you can go to the left at the start... correct me if I'm wrong)
Lemmings 2 - The TribesEgyptian 6 - RUPER'Z QUESTLING
Medieval 3 - ALL IN A KNIGHTS WORK!!
Outdoor 5
Shadow 6
Lemmings 3DFun 8 - Lemmings Inside
Tricky 25 - Breakout
Tricky 32 - Dot to Dot
Taxing 41 - Spaghetti Junction
Taxing 57 - T Minus Five And Counting (?)
Taxing 59 - Lemmtris
Taxing 60 - Death Slide
Mayhem 63 - Tower of Lemlab
Mayhem 66 - Family Tree
Mayhem 74 - Jelly Belly Islands
Mayhem 78 - Castle Peralus
Mayhem 80 - Final Maze
Lemmings RevolutionUnknown name. Click here for pic showing backroute.