Sorry for my ignorance but does that mean that a BMW 4x100 config will fit a Mk2 Golf regardless of the off set???
Depends on which BMW wheels you're looking at.
Golf MK2 Specs are:
The PCD (stud pattern) for all MKII's is 4x100
The centre bore is 57.1mm
Base offset is around +40 depending on the model.
From what i found on BMW 4x100 Wheels (OEM ones)
3 Series E21 = PCD 4x100, centre bore 57.1mm and M12x1.5 bolt thread. ET 12-20
3 Series E30 = PCD 4x100, centre bore 57.1mm and M12x1.5 bolt thread. ET 15-3
If it's these type wheels where it's same PCD, then you just need to double check CB. if centre bore is 57.1 as well then it'll fit on fine.
Offsets will matter depending on how you like the wheel to sit against your fenders.