I had mis-read part of smiggsy post and while my question on C22 above still stands, it is now asked out of interest.

Much more relevant is why if the correct C41 process for what were C41 films has worked on the leader, it hasn't worked for the rest of the film?

As I understand it the leader is in fact the same emulsion as the rest of the film but has simply been "zapped" with light. If this bit reacts properly to light and developer then why hasn't the rest?

We need you desperately P.E. Well the OP called smiggsy,Agx and I do to give us an answer