"88F" is just from what was painted on the entrance already - I doubt it's anything to do with 1623/88
there should be a photo, but it seems to be missing [Olly, Matrix 2 July 2024]
It's probably GSCB as the paint said VSS2, which seems to be some sort of nickname they had for themselves (or a subgroup)
meaning something like "the mad spit hammerers"
i'd guess 88F is their 6th entrance from 1988 - I think we've also seen 88H