I've been a GSA in two stores, and were allotted 2 GSTLs and 2 GSAs. Both of my ETLs have used GSTLs and GSAs interchangeably, to the point where I doubt most cashiers even know there's a difference. First store was a fairly predictable schedule, at least for closing shifts. Each of us had one closing weeknight, with rotating Fridays, and rotating weekends. Dayside shifts for me were either GSTL, SD, CO, or POG.
Current store is basically the same, except I'm part-time nights/weekends and thus nearly all of my shifts are GSTL/GSA, with the occasional close at SD. The other GSA prefers to close, and will usually get 4-5 closing shifts per week, sometimes an 11-7 Photo. We all still rotate weekends; it's me and my counterpart with GSTL on one, and the 2nd GSA and her counter on the other. Since the 2nd GSA volunteers to close, her counterpart GSTL therefore only opens on her weekends (which she prefers).
Right now, our schedule is kind of wacky, because my counter GSTL and I are both in school and have limited availability (i.e. she can only work until 11am and after 7pm on Mondays and Wednesdays, and I can only work after 5pm on weeknights). So, on those days, the schedule often looks like this:
GSTL 1.....7am-11am
GSTL 2.....9am-5:30pm
GSA 2 (me).....5pm-11:30pm