Well, it probably started out that way, then as years went by the empty weight and load capacity increased but the nomenclature stayed the same:
C-10 "half ton"
C-20 "three quarter ton"
C-30 "one ton"
C-40 "ton and a half"
C-50 "two ton"
C-60 "two and a half ton"
etc etc etc
My old C-50 GVW was 16K# but I think it only weighed about 6K# cab and chassis. Geez, half ton pickups weigh about that much these days.
In those days, there was no GCVW so I could safely ignore that
