I wrote a little script that should allow us to see what levels from the forum are in the code, and download all of them.
It's called download-all-levels-from-forum and it's in build-scripts. cd into there and run it, and it will download all levels, and copy any that have matching names over the existing levels in the code. Then you can use git diff to compare them. Any that don't match existing levels are left in a tmp directory inside build-scripts. Feel free to improve it!
$ cd build-scripts/
build-scripts$ ./download-all-levels-from-forum
Downloading levels into tmp/
tmp/48.rel Left or Right - not yet in the code!
tmp/37.rel Under pressure > levels/staging/water/Under-pressure.rel
tmp/50.rel Nice cup of tea > levels/development/water/Nice-cup-of-tea.rel
tmp/51.rel Nasty cup of tea > levels/development/water/Nasty-cup-of-tea.rel
tmp/32.rel Infiltrate > levels/development/water/Infiltrate.rel
tmp/49.rel Brollychuting 101 > levels/development/unsorted/Brollychuting-101.rel
tmp/30.rel Quick Dig > levels/development/water/Quick-Dig.rel
tmp/15.rel Uno > levels/06_small_world/19_Uno.rel
tmp/47.rel Don't Click > levels/staging/super-easy/Dont-Click.code.rel
tmp/53.rel Burst Water Main > levels/development/water/Burst-water-main.rel
tmp/44.rel Underworld > levels/development/water/Underworld.code.rel
tmp/46.rel Glass Half Full > levels/staging/water/Glass-half-full.code.rel
tmp/39.rel Water tower > levels/staging/water/Water-tower.rel
tmp/38.rel Underfloor heating > levels/staging/water/Underfloor-heating.rel
tmp/33.rel Waterfalls > levels/development/water/Waterfalls.rel
tmp/31.rel Fiery Finish > levels/development/water/Fiery-finish.rel
tmp/35.rel Dambusters > levels/staging/water/Dambusters.rel
tmp/40.rel Geyser > levels/development/water/Geyser.rel
tmp/42.rel Ghost versus pie > levels/05_arcade/01_Ghost-versus-pie.rel
tmp/36.rel Dive > levels/staging/water/Dive.rel