...even Apple's PR representatives on the tour had never visited it before...
And why would a PR representative have any reason to visit such an engineering lab, anyway?
I worked as engineering-level tech support at Intel, and while I did technically have access to some serious hardware testing labs (the shock/vibe test lab, for example,) I never had a reason to go, even though it was in the same building. While yes, the rooms may be "required access only", a PR person wouldn't really have any reason to be there, anyway.
For example, I know that the PR person who accompanied a
Tom's Hardware reporter through Intel's RF lab (along with the rest of the facility,) had never seen the inside of the lab before. And that's not even that secure a lab.