Ummm, actually… Based on the internal IDs, the Caterpie line was added all at once way after Venonat and later Venomoth. If there had been a readjustment or error, you’d expect these not to be in sequence (like with Wartortle losing its evolution and getting the first-design-phase Blastoise in its place). They may have decided to scrap Venonat, but then needed a prevo for Venomoth and kept it in despite the similarities to Butterfree, but having an evolutionary link between Metapod and Venomoth seems highly unlikely.