I have had this happen, and added the black stuff per instruction, and also added a few grams of dry CD-3 I have around from my mix from scratch days.

The idea was that the CD is what has oxidised in the part b. So add a bit in and see how it works. The stuff calibrated just the same as the good B concentrate with my lici colourstar analyser, standard test negative and the same paper batch , pulled fresh from cold storage.

I don't try to push it like new stuff. I figure I am pushing fate, and usually use it this way while I am waiting for a new order of fresh stuff to arrive.