The rules that use the vocabulary item "centers" are:

<i_f_v-pl>

opfor artillery battalion fire direction centers

opfor artillery battery fire direction centers

<specific_vehicle_type-pl>

command post carrier fire direction centers

<i_f_v>

opfor artillery battalion fire direction centers

opfor artillery battery fire direction centers

<specific_vehicle_type-not_creatable-pl>

command post carrier fire direction centers

<specific_vehicle_type-not_creatable>

command post carrier fire direction centers