Well, unless anyone can come up with something better, I think Matt hast he best explanation. That is, T buds really don’t connect to the cambium.
This has important ramifications for the often repeated “truism” that cambiums much touch. Far from it, cambiums can seem to be completely separated by some other layer (which is a different color) and still connect with callus tissue.
In my mind, this reinforces my experience that temps are more critical than cambium match and precise cuts.