Well I would expect the people they get in from user research to be playing the latest build, so that they can see if the changes they make are good or not. If they were playing an old build, then they could potentially have problems e.g. if they'd spent a couple of weeks working on something that gets scrapped after feedback. So if other people are playing the latest build, and bungie employees themselves are playing the latest build, then I don't see why they wouldn't let guests play it too. It's hard to say though, what with us being on the outside :/