>Sada was obsessed with pokemon from the past
>tried to create a time machine to send Master Balls to the past and catch them
>she apparently succeeded, but the "past" pokémon she caught are suspiciously identical to the fabled creatures present in the book she had since she was a kid
So they're not actually pokémon from the past. The time machine doesn't actually work. Instead it just turns Sada's dreams into reality and materializes her fanfic mons.
The same applies for Turo and the future pokémon in Violet.