I don't know and really don't care.
GK's role is cosmetic.
Just represents the game calculations + the roll dice of every game.
Like this DC for example who had 6 saves
https://forum.topeleven.com/top-elev...season-57.html

I prefer to buy a GK from scout or negotiations list with some low T price if possible.

but here there is a conversation about training GKs
https://forum.topeleven.com/top-elev...ain-my-gk.html