For Johnny Carson's tenure, with selected episodes officially being released on DVD, Carson Productions is becoming increasingly insistent on having unauthorized YouTube Carson clips removed from the site. To their credit, Carson Productions has been releasing a good number of complete episodes (usually the mid 70's 90 minute episodes) on YouTube for free viewing. And for the first time since 1992, the Carson shows are airing again on broadcast television, specifically the subchannel Antenna TV. When episodes started on Antenna TV, Carson Productions opened their licensing vault to the general public. New registrations are now likely limited to media personnel, though.
Even Jay Leno's era is not exempt from this; none of his episodes or specials have come to DVD, and the only legally-available options were a few Headlines and Jaywalking compilations on iTunes, which have since been removed from the service. His Tonight Show YouTube channel is also gone, so you can't even watch clips from his era on a legit YT channel.
Thanks to the 2010 Tonight Show debacle, NBC will never release any DVDs or digital downloads of The Tonight Show with Conan O'Brien. In fact, the only acknowledgment of the show at all as of late seems to be a split-second showing of O'Brien's name as part of a list of past Tonight Show hosts that was seen during various promos for Jimmy Fallon's then-upcoming premiere.
Much of Steve Allen's tenure is gone, although the premiere seems to exist.
Allen: In case you're just joining us, this is Tonight, and I can't think of too much to tell you about it, but I want to give you the bad news first: this program is going to go on forever.note (Okay, so he was talking about the show's night-by-night length, but still...)
Much of the first ten years of Johnny Carson's version, due to tape reuse. 1972-92 are intact.
Unintentional Period Piece: Unavoidable, due to the monologue covering current event topics which can be head-scratching to younger viewers. This can even extend to the hosts themselves: In some shows during 1982, Johnny Carson complained about being in the news a lot lately. If you weren't alive at the time, he was referring to an incident where he was pulled over for drunk driving.
Jack Paar's version:
Writer Revolt: Jack walked off during the February 11, 1960 show after discovering that NBC censored a joke the previous night regarding a lady looking for the "water closet" who was directed to a wedding chapel due to her only using the initials "W.C." (the network cut into a news report over the joke). His sidekick, Hugh Downs, took over for the remainder of that telecast. Led to a Funny Moment when Parr returned a few weeks later with the words "...Now as I was saying..."
In 1983, a Clip Show series called Carson's Comedy Classics was offered to local stations. Each half-hour episode consisted of two or three extended segments, usually "Mighty Carson Art Players" skits and/or segments with Carson characters such as Carnac and Aunt Blabby, plus shorter segments (i.e. commercial spoofs).
Also applies to the Antenna TV run; as NBC owns the name "The Tonight Show", a new title sequence had to be made, referring to the show as simply "Johnny Carson". Though unlike Carson's Comedy Classics, these are the full episodes.
Milestone Celebration: Prime-time specials to observe his anniversary – 1972, to celebrate Carson's 10th anniversary of hosting the show; 1977, for his 15th; and annually from 1979-1991. The first special was rather limited as far as showing "classic" highlights, since most shows had been erased or recorded over, although famous moments – i.e., Ed Ames' tomahawk throw, the Dragnet parody, Tiny Tim's wedding and others – were preserved and shown. The later specials had more archived clips, since all shows produced after sometime in 1972 exist.
Jay Leno's versions:
The Pete Best: Branford Marsalis was the bandleader before Kevin Eubanks.
Originally, Leno's post-Tonight project was to have been an American Top Gear. Leno actually turned down this idea when it was initially proposed to him, realizing that what made Top Gear work was its non-commercial carriage on The BBC...and an NBC version would be filled with Product Placement and Executive Meddling. There was also some concern from BBC America that an American version would cannibalize ratings of the original on BBC America, where it's very popular. An American version did eventually premiere on the History Channel.
The Tonight Show Starring David Letterman could well have been the case, but Letterman assumed he'd be the successor, as did Carson. Leno (or his manager, Helen Kushnick; nobody's actually really sure) actively but quietly campaigned to get the job from the people that actually made the decision, however, so he got it and Letterman went to CBS.
Conan O'Brien's version:
Executive Meddling: The entire debacle that NBC created by trying to reshuffle their schedule by moving The Jay Leno Show from an hour at 10 to a half hour at 11:30 and moving Tonight and Late Night back half an hour. It was unclear if Last Call would remain on the air.
What Could Have Been: The episode with Teri Hatcher as a guest was never aired; it was never finished because Conan was rushed to the hospital for a concussion that he suffered during a foot race with Hatcher.
There's an element of Could Say It, But... here, as Conan had been given a gag order prohibiting him from badmouthing the network. He took to lampshading this in his last few shows.
One of the writers did a sketch so against the network it seems Conan didn't want to say it.
Conan deliberately ratcheted up the cost of his show, thanks to a contract loophole that allowed him to do whatever the hell he wanted on NBC's tab. Starting with a Bugatti Veyron mouse and the 2009 Kentucky derby winner in a mink coat. Of course, most of it wasn't real... except the expensive songs and their royalties.
Jimmy Fallon's version:
Throw It In: The theme song for Jimmy's run was created entirely on accident. According to Questlove, the Roots were just screwing around to test out the studio's speaker systems and the recording of it got mixed in with the batch of songs they actually did write as potential theme songs. Jimmy heard the improv song and decided that was the theme song.