Nepster and Wafflem did most of the work on the conversions. IIRC, they made an effort to confirm the levels were solvable, rather than just blindly converting. Levels that were just barely unsolvable (eg. should be solvable but it doesn't work out due to subtle mechanics differences) often were tweaked so they would be solvable; while I think those that were far from solvable (eg. due to relying on glitches) were removed.