I was under the impression that the IVs/Vs and the reintroduced TBird had the same pups initially. Then the IV/V fell by the wayside and the TBird carried on getting eventually vamped up versions of the TB pup. To all intents and purposes the IV/V should be a modern ergonomic TBird at its outset (Phil Jones, who designed it, told me) it wouldn't have made sense to have consciously given it different pupps to what it should emulate.