The thing is, 'off limits' areas may be in effect easter eggs intentionally put there by the mappers. They let you get there but are also deliberately made difficult or require certain maneuvers not just a single mantle or climb. Even if they seem a little weird like bouncing off a light. Of course the difference is whether or not you can glitch inside of walls and such to make yourself invisible while you shoot people. Especially if they are solid one way walls.
IMHO the test is whether or not there are one-way walls or similar game geometry like rocks or trees. If you can see one, or at least significant ones, then you shouldnt be there. There is a map where I recall a long row of hedges next to a building that are one-way if you stand right up against the wall. Otherwise the enemy sees you. Is that intentional or is that a glitch? All depends I suppose.