To answer your question, yes probably most of the time GSAs who promote will do so within their own store... HOWEVER, just because someone is a GSA doesn't mean they should be a GSTL.... it is actually frowned upon to promote someone within the same team (any front end team member to GSTL, any flow team member to Flow TL)... If the STL was focused on best practice and team culture and a GSA passed interviews, they would try and place them in any area other than GE...