Just a curious thought, are most of the older premium packs prototypes?
no, they are just unique things and stuff like that, Ex (now removed) the CEV premium and the AV-8A
They can be anything.
Porsche Tiger prototype, Ru 251 prototype, KWIC captured tank, PzBefWgIVJ command tank, PzSfl1c tank, etc.
Not all, the Centurion AVRE (its now a GE prem but was a pack) is a modification that was used until the late 1990s, the version in war thunder is the kind used in desert storm.
They tend to be famous or unique vehicles, some are prototype, some are just unusual modifications