Currently GSS has only one series format, which I will call ‘Sequential’.
Each new addition to a series, behaves as chronological ‘next chapter’ or ‘sequel’ to the previously posted entry.
It has the options “previous chapter” and “next chapter” in arrows at the bottom of the submission.
A ‘Compilation’ format would function as a more basic anthology of stories. i.e. not enforce or suggest chronological reading. You would use this non sequential series format for series that are collection of independent stories that share a theme, but dont need to be read in chronological order.
Instead of “previous/next chapter” in this series bar, It could have one button for returning to the main series screen (so you can pick the next stand-alone story you like the look of) and one button for immediatly going to a new random story in the series.
In time to come it may be feasible to make the random selection ‘know’ the ones you’ve already read. So by continually clicking “go to another series entry” (or whatever you call it) you’ll eventually get around to all the entries in that series.