In the later series when there were 5 instead of 3 limited editions, the "rarest" limited edition had only 250 printed. For example, Squish Bone from Series 4.
UFT were so expensive that I couldn't bring myself to collect them, so unfortunately I don't know anything about them really.
Maybe there are collectors who just want to finish off their collection, not sure otherwise.
I know but those are gone as well maybe they could make a new spin-off series like the grossery gang
Interesting, how are you still collecting them?