In my eyes a Restoration is when there are enough game files to make a mod to simulate something Bioware/Obsidian wanted to achieve, however, when they get too far and require to make new content that isn't what Bioware/Obsidian intended that is when it becomes custom content. Examples of "Not Restoration" Restoration mods include M4-78EP(Barely anything was left to restore so not wanting to restore 10 minutes worth of boring gameplay they made a whole lot of new sidequests for the mod to add life to both the mod and the planet), Sleheyron (Everything in this will have to be custom content due to the extreme lacking of cut resources to use), GenoHaradan Legacy (The GenoHaradan were supposed to be in the Jekk Jekk Tarr but have been moved to the cut rooms on the docks to fit in with the plot) and the Fragile Alliances falls apart scene in the Extended Enclave (That was supposed to happen after the GenoHaradan plot line on Nar Shadda but was moved to after the enclave sequence to give it some sense, also Sion was supposed to die at that scene)
Some things like the Black Vulkar Sublevel and the HK-50 Factory simply needed minor fixing and/or a few edits here and there to get it working (Though I'm sure the restoration teams of both K1R and TSLRCM will love to throw their 2 cents at me and say the words "minor" and "few" are a long shot away from what they really were). Isa the Sith Apprentice in K1R, in my opinion, was not worth restoring due to them having to make that awkward lying down NPC from scratch though I must give points for successfully restoring it. I also believe the Pazaak Tournament was custom content as well but that might be me not wanting to admit all of that was lying around in the game files.
I hope this is enough to add to this thread