Currently on the site they are all listed with "Typ AB9" as chassis code, and generation (mk) number go up to 7 (VII) for some models, but not all, I assume a mix between the generation and the restyling: the restyled 2nd generation were named G3 and G4, the 3rd generation was G5 and then G6 and G7 when restyled.
According Wikpiedia there are only three generations, with restylings:
https://en.wikipedia.org/wiki/Volkswagen_Gol
https://pt.wikipedia.org/wiki/Volkswagen_Gol
AB9 seems the code name of the 2nd generation project.
First one would be Typ 30
Second one is listed as Typ 37/5X/5W, I'm not sure to what they correspond. Maybe the facelifts, so 5X = Gol G3 and 5W = Gol G4?
Third (current) one would be Typ 5U
Maybe we could use the mk field for G1 to G7 (having it displayed as G+number then).
So I'm waiting for some input before starting to clean these