>>15327702Except that's not what happened. What happened was:
-Ultimate weapon was fired off
-It irradiated tonnes of stone, causing them to release radiation that synergizes with certain pokemon.
The pokemon doesn't have to have existed then to have something that happens to synergize with it. The only reason for that to be the case would be if those stones were made specifically for the intent of mega evolving those pokemon, which is like assuming that fire stones were made to specifically evolve certain fire types.