Ascended Fanon: Originally, there were rumors circulating around the Internet that one of the higher-ups at Nickelodeon sent the okay for the production of new seasons of several old 90s cartoon shows, including Rugrats, Hey Arnold!, Rocket Power, Doug, and several others. Though false, the rumors generated such a buzz that the execs did pick up on it and decided to create the late night block for TeenNick.
Within the block, CatDog seems to be getting just a little bit more attention in advertisements than other Nicktoons.
Some have accused Hey Arnold! of becoming this for the block. While most of the cartoons shown from 10:00PM-11:00PM are supposed to rotate each week, Hey Arnold! seems to fill this slot every other week, and whenever the block has time to fill, expect to see Hey Arnold! there. (This may be because A: the show has a huge fanbase and B: Nick is making up for having treated the show badly during its' final couple of years.)
Nick finally takes advantage of their legal right to show pre-sale-to-Disney episodes of Doug.
While Nick has the airing rights to the whole Power Rangers franchise, most people probably weren't expecting Mighty Morphin' Power Rangers to air in any capacity on the block. It ended up airing as part of the "Mighty Morphin' Weekend" event to celebrate the 20th anniversary of the show. No clue if it'll return along with the rest of the 90s Power Ranger series.
Edited for Syndication: One of the drawbacks of airing 1990s reruns of kids' shows 20-odd years later. TeenNick cut out the musical performances from All That due to music licensing issues, and Rocko's Modern Life is still shown edited since Nickelodeon lost the original masters at some point. (Similarly, these versions are also on the Rocko DVDs.) Which becomes Fridge Logic, since the original masters are available on Nick in Canada. All the American Nickelodeon has to do is ask Canada nicely for the masters (hey, they already hijacked You Can't Do That on Television for themselves, so why not?)
When the KaBlam! episode "Not Just For People Anymore!" aired on the block, the Lava short was edited out of the episode, along with the Henry and June wraparound leading into it, as Nick no longer has the rights to the short (they however forgot to edit it out of the credits of the episode, though).
Weinerville had to have the cartoon segments cut out from the episodes as none of them were owned by Nick. They were replaced with Rugrats episodes to fill the slot.
Disney launched a YouTube channel showing their old work (Not literally a block, but a channel to watch the old shows as well as new ones too.), and later, brought a similar block for Disney Channel... but on Thursdays only. (And after that, release a few blocks of classic shorts to Netflix.)
For the 25th anniversary of the first three original Nicktoons (Doug, Rugrats, and The Ren And Stimpy Show), The Splat aired the first episodes of all three episodes in the order they originally premiered (though in the case of Doug, it's second episode- only because that was the one that premiered first back in 1991) on their original premiere date, August 11. The three following weekends ran marathons of each show, along with having the cast and crew of the shows answering fan questions on the big orange couch. To further celebrate, the following weekends have had a different Nicktoon each weekend taking over the 11 PM hour.
KaBlam! is scheduled to debut on The Splat (after eleven years of not having regular reruns) on the weekend of October 8-9, 2016- which happens to the be the weekend prior to the day the show turns twenty (October 11).