If the definition of Intenral Out of Bounds is that a part of the course is out of bounds when playing a differ to hole, Oakmont and many others have IOB. The holes on one side of the turnpike are out of bounds when playing the ones on the other side. Most course that have holes on opposite sides of a public road have that. I don’t consider that Internal OB. Neither do I consider parts of the property that are not holes such as driving ranges and clubhouses.
This makes total sense -- so if you hit it across the road on accident you don't play back over the road deliberately and cause more danger. But I do not remember ever seeing it as a local rule on a scorecard, at Oakmont or anywhere else.
The discussion reminded me that the 14th hole at Sterling Farms [where I grew up] is OOB when playing the 13th, a par-5 which doglegs around 14. I was actually remembering it backwards, because the 14th is a par-4 where you have to drive it between two ponds, and there would be some temptation to play that shot to another fairway also, but there's no option that really helps on that one.