there are a lot of Mystics I collected soul stones through the events but not enough to get the card.

When I open the 4th box of an event I only get soul stones of Mystics I already have. And when I open Mystic Boxes I get only Souls of Mila, Olivia, Zoey, Isabella and Kelly but not from Mystics of former events.

So how will I get the missing Soul Stones of Mystics from former events?

And will be there any chance to complete the stories of former events, I also have a lot of incomplete story lines...?