I don't know why Italians keep them in separate classes. The aim of this A/B/C/T/D letters when they were creted by FIA was to allow different vehicles to compete in the SAME class :) The letters only distinguished vehicles made under different possible option within the same class (A, B, C was for engine size, T was for turbocharged and D for diesel engines and all of them had somewhat different weight limits or other modifications to stay ballanced within the same class).

