That’s is not correct. The C are Alnico in the cast pots. The 414E are ceramic.
414Z = Alinico, rear-mounting frame, welded magnet pot, 16ohms
414A = 414Z with magnet cover
414B = 414A but 8 ohms.
414-8B = 414B with new cast frame
414-8C = 414-8B with cast magnet pot. The 414C is 3 db less efficient than the 414A.
414-16C = 414-8C in 16 ohms
414-8E = 414-8C with ceramic magnet. No magnet return pot
414-16E = 414=8E IN 16 ohms.