Why are pokemon like yanmega,mamoswine considered johto pokemon?

I thought they were introduced in the sinnoh region
Maybe there was a yanmega or mamoswine during the johto anime series but just didnt show up? Im assuming that

no yanmega and amoswine were never shown in johto, only in sinnoh, and no1 ever classifies them as johto pokemon
im guessing that you think this because they are evolutions of johto pokemon which would explain a lot

moved to pokemon discussion

dialga:uhh no they were in the johto dex, same goes with lickilicky,ampibom, and tangrowth

They were essentially an add on to the Heart Gold, Soul Silver games, the same way that Pikachu was on the Ruby and Sapphire dex