And I always thought the Z in Mirak was due to the following...
M = Monster
I = ISC
R = Rommie
A = ???
K = Klingon...
So, when faced with the choice of starting the ships with the obscure "A" for Mirak, or going with the "informally used" Z from SFB, they chose the second...
On the BCx issue, the thought is this. On the bottom of the secondary hull, there's a weapon's pod (dorsal turret). Depending on what weapon they put there, determines what class it is...
F-BCG = "guided weapons" model, as it has 2 B-racks in the dorsal turret
F-BCF = "Plasma F" model, guess what it has instead of B-racks...
F-BCJ = "New Jersey" class. Photon boat with shock. Why they call it the New Jersey class (due to frequent breakdowns???) is beyond me, but there it is...