I've been sitting on this question for years...
What are the official titles of all the LPU CDs? Linkinpedia labels all the releases as "LP Underground (_)" but the packaging for many shows wildly different naming schemes, and Discogs/MusicBrainz also use even more different naming schemes, often also omitting "Linkin Park" from the title entirely (though I think this is mostly due to a lack of understanding that the fan club is called LPU). And metadata really matters to me. Looking at my own collection plus images from Discogs, etc for the ones I don't have, the titles read:
LP Underground 2.0 (or more accurately, "LP Underground" [2.0], but that's nitpicky)
Linkin Park Underground (main cover says this, inside cover refers to it as "LP Underground 3")
Linkin Park Underground 4.0
Linkin Park Underground 5.0
Linkin Park Underground 6
LP Underground 7
No comment on 8, surprisingly it's the most straightforward
Linkin Park Underground 9: Demos
LP Underground X: Demos
Linkin Park Underground Eleven
Linkin Park Underground 12 (per spine)
Linkin Park Underground XIII
Linkin Park Underground XIV (per additional merchandise)
Linkin Park Underground 15 (not sure about this one)
Linkin Park Underground Sixteen
Does this really matter that much? Probably not. Does it still bug me and burn for a definitive answer? Yes. Thanks for your attention and have a nice day.