I've tested various split bathes on C-41 and ECN-2 films.
What I've found is that there -has- to be development (low contrast) in bath A, if only a little bit, otherwise, very thin negatives from very low EI's every time (and bad colour).
The carry-over amount in the emulsion is simply not enough to have developing only occur in B. Even with vastly increased developer levels in bath A.
And with this.. you can alter effects and colour by varying time in Bath A.
Some people have left out the sulphite in Dignan's formula and found they got essentially nothing on their negs. When they finally tried it with the sulphite, it was greatly improved.