I just read One Piece Novel A and found out some facts about Bb. So, Ace asks Tatch and Bb if they know who gave Shanks his scar. Tatch says he doesn't know and Teach says he knows then says he was joking. He then adds that he could kill Ace and steal his devil fruit and then he says that he was joking again.
So my theory is that Teach already had the lower to steal devil fruit powers. And that he was just waiting for the devil he wanted. He saw how powerful Ace's fruit was and wanted but it was the one he was waiting for, so he waited a bit more. Which could mean that if he had managed to get Ace's body after the war he could have stolen his fruit power.
Another fact that could support this is that Marco said that Teach's body wasn't normal + the comment Buggy made on Teach never sleeping. This could be the reason why Teach could steal devil fruit power and keep them to himself or give them to others like Shiliew.
This may the wrong but I think Oda is trying to hint at something in Novel A.
What do you think, am I overthinking this ?