If the secret is sexual abuse, then there's one place it could already be read into before BftC, and that's when Winick wrote the Jason/Mia fight in Green Arrow. Jason tells Mia that Ollie is just like Bruce, rich and privileged, and will never ever understand what Jason's and Mia's life was like, but Jason is just like her. "I know that sometimes you've got to do the bad thing." And it could refer simply to the fact that Jason stole to survive on the streets, but given what Mia's life was like, I think the other reading is far from unsupported.