IRL, with your GFE, BB and SS would be the norm.
In companion life, GFE means different things, rarely BB. SS sometimes an option. I think some companions say "not GFE" to ensure there is no confusion (about BB). I interpret GFE as, will treat me like a boyfriend and not a business transaction. Btw...if you treat a companion like a GFE, be respectful, treat them nicely, even perhaps bring a gift, they will treat you better as well.