The OTHER "gang" mutants

[sdp]

So, watching all of the old toon dvds to hype me up for the new movie, today I watched the 5 episode pilot, and i've always noticed this, Shredder mentions that if two mutants can't do the job maybe others will. He then mentions he hasn't perfected mutations yet and we see a screen of the other "gang" members that were with rocksteady and beebop on the first episode turned into mutants.

When Shredder tells Splinter of the retro-mutagen gun he uses one of the new mutants as an example, I always thought that Shredder ended up de-mutating them but later on the last episode of the season you see all of the gang as mutants in a cel, so obviously they are still mutants. How come Shredder never used them?

i wonder what happened to them.