There was going to be a tenth player in the Mario Power Tennis tournament, but they dropped out.
They were going to have a guest player for Kirby's Return to Dream Land, but they couldn't make it because of a scheduling snafu. It's implied by a comment of Chugga's that the guest player was going to be JoshJepson.
In his intro video, Chugga talks about several alternative names for the group they considered. Some of them are also referenced in the main videos, such as "Press Start to LP" ("Press L to P!") and "Splitscreen Shenanigans".
According to Jon in episode 12 of Kirby's Return to Dream Land, another name idea was "Shark Uppercut", which was literally something random Jon just thought up out of nowhere.
According to Jon's Formspring, LP#7 was planned to be The Legend of Zelda: Four Swords Adventures, but because Josh, Tim, SuperJeenius, and Pcull44444 were playing that game at the time, they decided to hold off on it until later.
In his solo channel, Chugga said there was planned to be a Kirby's Epic Yarn LP. However, they called it off because they thought the game doesn't work well with two people. (and because they couldn't kill eachother) Later, Chugga LP'ed it himself, though he did make one multiplayer video featuring Jon.
The Mario Party 1 LP was recorded at Magfest 2011.
New Super Mario Bros. Wii was recorded at PAX East 2011.
Super Smash Bros. Brawl ("Subspace Emissary") was recorded at E3 2011 and at Jon's home in Canada.
Mario Party 2 was mostly recorded at Jon's house, and the rest was at Pax East 2012.
Kirby's Return To Dream Land was recorded between two Paxes.
LittleBigPlanet started at Pax Prime 2012, and continued at Chugga's house.