An S1 of itself is still going to be an S1. If you selfed an S1 and took pollen from that and pollinated the original mom, then you would have legit S2's and they would probably be a real close representation of the original cut with less variation.
I understand that, but there never going to be anything but an S1 until another plant is introduced aside from "brother/sister" plants. It would be totally pointless to breed "brother & sister" from the same S1's. Isnt that why breeders bx is to solidify genes and breed in/out certain traits? Those genomes never change unless you do.
You will get different variations from S1's compared to the original that the S1seeds came from. If you plant 6 GG4 S1's and you find one that is close to the original cut of Glue, then selfed that, and pollinate the original mom you will be dialing in the desired traits making your seeds a closer representation of the original cut. If you bought true S2' or better, it would be a safe bet that your gonna have some fire plants real damn close to the original GG4 cut.