The numbers at the end have to do with the numbering system they use for achievements in general. The 1 at the end of STK1 probably indicates these 10 are for the first DLC in the season. Not that there couldn't be additional seasons. If I were Firaxis aiming for a GaaS model, I would try to run more than one season. It could be that we only see a portion of the remaining series regulars with the last being held for a second season.