The number in parenthesis is the stock of limited supply maybe? for a guess
CORE, AUX, Captured, Prototype, and Gift.
A. CORE of course is your primary nation, and you have unlimited supply of units available.
B. AUX typically is for nations also assigned for your use, such as Italy. These units provide temporary increase to your army strength on any given scenario. A very popular tactic of Spanish Civil War testers is to rely heavily on supporting Italian CTV units to bolster their early scenario fighter air force before swapping over to much more potent and permanent He-112s and Bf-109Bs as they arrive toward the middle of the Spanish Civil War.
C. Captured units retain their limited spare part supply of the base Panzer Corps 2 game, with one extremely important caveat: It's now possible to earn huge stockpiles of captured spare parts as rewards for turning in Commendation Points. This should greatly increase the ability of players to field captured units without immediately worrying about running out of spare parts. Of course if you don't continue to capture enemy units on your own, you will eventually run out of spare parts.
D. Prototypes are generally unaffected. Their implementation is the weakest link, because unlike captured units, there is no way a player can go and hunt for 'more spare parts.' Which brings us to...
E. Gifts. Gifts is the primary replacing mechanism over Prototypes. A gift unit behaves like a combination of CORE and Prototype by keeping the best traits of both. A gift unit has NO spare part limitation, like a CORE unit. A gift will always be a unit you cannot ordinarily purchase, sort of like a Prototype unit. A gift unit can come from any nation's equipment table... including enemy aircraft. Galland just might get that squadron of Spitfires he requested after all these years! A gift is yours to keep indefinitely, and overstrength as you see fit. Be warned though, if a Gift unit is ever fully destroyed, there is no getting it back. So be extra careful with these very special reward units!
(i could be wrong, my replies are 50/50, sometimes i'm right, sometime i'm wrong, but hopefully it's correct
