According to Hans-Otto Neubauer, writing in the Georgano Encyclopedia:
Z2 was a 6-cylinder 1100 cc opposed piston two-stroke
He seems to say that Z4, Z6 and Z9 were 2-cylinder and Z5 a 4-cylinder (1.5 litre) two-strokes
Z13 was an 8-cylinder duplex two-stroke (parallel pairs of cylinders with a common combustion chamber) of 1500 cc and 60 h.p. output
Still a few Zs missing, and no mention of Z12.
Might be more in the two-volume book that I cannot bring myself to afford!