Many thanks, Sylvia! I had been looking for section paragraph, but couldn't find it, and it's obvious I skipped over it carelessly.
Since every skater/team in the top 24 seasonal best or ISU rankings who is planning to skate senior GP already has two spots, and every Jr. Worlds or GPF medallist who is skating seniors has at least one spot, by section 7.6, any replacements can be made from any skater or team who competed in one of the events used for top PB, since, by definition, competing once gives a personal best, and the PB needs to be in the top 75 or higher (LOL).