I've looked high and low so apologies if this is state elsewhere in the manual or the black book.

In running z12, I see that the algorithms are labeled BB, CY, HP and VO, What do these abbreviations mean?

Guessing here BB = Black book, CY = ??, HP = HighPass, and VO, VolumeOptimized. (total guesses!)

Does anyone know what these abbreviations mean?

Is it also safe to assume that 2 of the algos are from z1 and two are from z2?

They are only letter codes and have no real meaning. ES, HU, LP, LS, VO belong to Z1, and A2, BB, CT, CY, HP to Z2.

Thanks JCL!