Hi
They *should* be in 80 pace sections (per page 11) but I personally don't have an issue with an opponent extending a single TF to cover the depth of an element of Bg. What are talking about here - maybe a maximum of 2 extra AP?
I have re-based my Bg to be on 80 pace squares but I wouldn't expect my opponent to be penalised simply because he hadn't got around to re-basing his Bg. I recommend you check with your opponent before starting the match, and phrase your question with the end in mind : "You don't mind if I.....do you?" There response might dictate how you play the game!
Andrew