If photos of the Y-20 came up merely days after reports of taxi runs, then we can safely conclude that the security at XAC isn't exceedingly tough. If the JH7B flew such a long time ago and no photos have been posted of it, then I'm starting to wonder if reports are accurate or not, and whether such a project is a major thing at all.
It's most likely because JH7B looks almost exactly the same as JH7A so no one took notice when it first flew. Yanliang's security is indeed tight, but the best security is the self censoring of military forums, J20 is testing at the same airfield as Y20 yet no one has seen any photos of it.