On the subject of shortcuts, I know of one in The First Encounter that I deliberately didn't use. In Level 4, Valley of the Kings, go to the room after the boss fight, right after you get the rocket launcher. From here, it's possible to rocket jump into the sky and noclip all the way to the very end of the map.
That one is definitely Out of Bounds because you're just floating through nothingness

So that one wouldn't be allowed for SDA.
In Metropolis, there you just walk on the side of the level a bit, that's not OoB because you're basically still walking on a solid level part. Same for Karnak.
Most levels are 1 big place, so if you can get over a wall, you're still in the level. But Valley of the Kings is different because it's mainly made up of rooms (The same with Hatshepsut/Sand Canyon/Tomb of Ramses/Oasis and Sewers).
The other levels basically consist of 1 big room/level, no problem getting over walls in those levels since you will still be IN the level
