I've never seen Z refer to "Zulu" in any SureFire text...
"C" does not mean CombatLight. It means Centurian. It's just a letter going spare at the time.
Not all Millennium Series models are "CombatLights" (only the M2 and M3/M3T have CombatGrips).
Because SureFire have been around for so long there are many historic systems that have not been superceded.
Use of an "A" could mean:
A2 - flashlight.
A19 - adapter body to convert 6P to 9P etc.
AN14 - adapter body, Nitrolon, to convert G2 to G2R.
M900A - standard bezel version
M500AB - TurboHead bezel version
X200A - original version
SF323AC - Stock-isolated battery stick, three-SF123A (aka 9V)
618FGA - No idea what it means. Perhaps to identify it has a Shotgun WeaponLight?
Does "L" mean LED? Sometimes!
L can mean Lamp Module (L60, LM90, LU15 etc), Laser Module (L72 etc), LED bezel (KL4 etc), LED flashlight (L1 etc), 5" long pressure pad (suffix L for example 650-0505BL), or just "Light" (6BL BatonLight etc)
"K" means "Kroma"? No yet at least!
At this point "K" means:
"Kit"
KT3 (TurboHead Kit #3)
KR22 (rechargeable Kit for G2 with UK powersupply)
KM501 (conversion kit from M500A to M500B)
or
K also means stiffened tape pressure switch waterproof to 30 metres (628FK)
These are just a few examples of why the nomenclature is not simple or easy!
Al
P.S.
"G" means a disable rocker switch on a WeaponLight forend (for example: 618FGA), but, a disable rocker switch on a Classic Universal WeaponLight is "D", as is the disable shuttle switch on a Nitrolon, Military or Millennium Series handgun WeaponLight (whereas a disable flag switch on a Classic Universal WeaponLight is "S")
So "G" means Nitrolon? "N" is used for Nitrolon when it is an adapter body (AN14) or a Nitrolon version of the 8AX (8NX), but "P" means Nitrolon when referring to handgun WeaponLights!
P.P.S.
There are so many questions to ask that we'll never get answers for!
Its best not to get too worried about it all (trust me)