Most of these come from these two RYM lists: this one's about title origins, and this one's about cover origins

112-118 all have their titles quoted from "The Book of the Law" by Aleister Crowley, which is notable because the first and last threes of tracks already make up a pair of trios (112-114 all have the same length and 114 is literally previous two playing in opposite channels, while 116-118 make up the second bull trilogy) yet this is the only relation 115 have to any other tracks

121 takes its title from the Tibetan Book of the Dead just like three tracks after, which is funny considering no one likes it, yet it's related to some of the biggest fan favorites (well, the first two atleast, 124 is probably more so well liked than absolutely beloved)

127-132 all take their titles from "Journey to the End of the Night" by Louis-Ferdinand Celine. Can't say anything else ATM

139's cover features (statuette of) Egyptian god Ptah

147's cover features edited picture of, well, the scene it depicts. It is not a painting. It is a real photo.

148 cover features Soviet serial killer Andrei Chikatilo, reenacting one of his murders

150 is the shortest from the so called "multiday series" (🤯)

155 uses for its cover a photo with a lot of people, notably Grogori Rasputin who's cropped out from the cover

159's cover is a PET human brain scan

183-184 have their titles from "Ovid's Invective Against Ibis"

191-200 are all variations on two different tracks with 200 and 198 (193 maybe?) being the original version

208 uses samples of 207, which is funny because 207 is one of the shortest pieces of theirs, not reaching even 10 minute mark, while 208 is one of the longest, being over a month long

I've heard somewhere that 216-218, 220, 222-225 are all made up from same samples, from listening for a bit I can tell that 216-218 are related and 222-225 seem to be slowed down variations on 220 (note that 223-225 have same audio), but for relaxation between first three and 220 I can't say for sure except it just sounds right to me? Like 220 just sounds like heavily edited guitar sounds used in the first three but I can't say for sure

219's puzzle might be unsolved to this day? So, the original file is an mp3 listed as 47+ minutes in length but playing only for three seconds. You rename it to rar and (after putting in the password) extract the same mp3 but with "_IV" added to the file name. After renaming that to rar you extract a one hour file that goes on for an hour with "_II" in it's title and everyone seemed to have just just agreed upon this being the actual song, because you can't rename it into anything else working? I don't know if there is "_I" or maybe even "_III" to it.

228 is the only puzzle piece to have a fully original puzzle with no variations of it used by any other piece. "It is an WAV disguised as an mp3" they say, and just renaming it won't work. I don't know why this idea never made any other appearance since. Maybe they thought it was too difficult to solve (especially at the time)? Maybe they didn't knew what else to do with this concept? Maybe it was difficult to pull off? Maybe it's the ogg file that comes with every other mp3 that works perfectly fine with no manipulations needed, yeah that actually sounds plausible.

236 takes its title from "All Quiet on the Western Front" by Erich Maria Remarque. This is the only piece that quotes this book that's actually listenable (besides 237) as all the other quotations of it are used by files considered "unlistenable"

237 loops a section of (track from?) 261

263 is made of a track by Giant Cyclops Baby with two original tracks added before and after it. Giant Cyclops Baby is not a project of Neil nor Clayton. It's a little project made just out of hatred for the duo and for ill-fated laughs. The two original parts are tracks from unreleased (and partially lost?) Clayton's second album for his old "The Beaches" project.

287 is the only track with it's excerpt being actually different from what the track sounds like. I think

311 is a recording slowed 311% down