I thought only the 3rd evolution stage of Pokemons have 3 EV yield.But volcarona is just the 2nd evolutionary stage of larvesta has has 3 SpA.Shouldn't it be 2 SpA EV Yield?
EV yeilds have nothing to do with how many stages a Pokemon can evolve on. Volcarona would have a yield of 3 Special Attack, mostly because of it's exceptionally high Special Attack. If that's how Game Freak wanted it, that's what they'll get. They are the creators, after all.