When is the level of NPCs in a dungeon determined?

[HideInLight]

I wanted to see if I can raise the levels of some dungeons with the creation kit, I tried saving the game before entering the dungeon for the first time but the changes I made in the CK didn't appear to take any effect. All the NPC's were still in the same low level range as in vanilla. My theory thus far it's determined when you discover the dungeon, not when you enter it, but I could be wrong.

[David Brasher]

To the best of my knowledge, NPCs spawn when you enter their interior cell or exterior 5x5 block of cells. If you were to enter a dungeon and leave without killing anything, and then installed a mod which makes all the spawn points spawn horrible hard bosses, when you went back to the dungeon, all the enemies would just be normal strength. But if you went and entered a dungeon you had never been in before, or had cleaned out more than three days ago, you would find a dungeon full of tough bosses.