Author Existence Failure: Not strictly related to Bridwell, but the reason the animated series was spun off to Clifford's Puppy Days and the main show was abandoned was because of John Ritter's untimely passing.
Casting Gag: Having T-Bone's friend Hamburger being specifically voiced by Kenan Thompson. Also their fast-food inspired names are a Shout-Out to the Good Burger sketches seen on All That.
The Danza: Frankie from "Little Big Pup" is voiced by Frankie Muniz.
Development Hell: Universal and Illumination Entertainment were planning to do a film based off Clifford for a 2016 release, but nothing came out after the announcement. By the time said year came around, it was clear Universal no longer wanted anything to do with the film anymore, as it was revealed their rights had expired and the project moved to Paramount.
No Export for You: The iPhone and iPad game are this to South America and Asia, as are the releases on the Leapfrog consoles. Most of the toys, however, are North America only, especially those that are not made by Scholastic themselves.
The Other Darrin: They did not replace any of the characters on the the show in the strictest sense, but in the original 80s specials, Emily Elizabeth was voiced by Alyson Court. On the 2000s series, she was voiced by Grey De Lisle. Possibly also Lampshaded by the fact that both had a vastly different narrative structure and art style from each other.
Outlived Its Creator: Norman Bridwell passed away on December 12th, 2014. At this point the TV show has stopped and has had no new episodes since 2005, but he has two books that is still unpublished. Also, there's the movie, still in development, having originally been announced for 2016.
Recursive Adaptation: Inevitable. Books that were based on the TV show were published once the show became popular. Given that the show is based on books in the first place, yeah.
Screwed by the Network: Similarly with what happened to Arthur and its 12th through 15th seasons, Clifford's Puppy Days was originally produced in 16:9 widescreen HD. For whatever reason though, PBS aired an SD center cropped 4:3 version of the show instead, even on every HD PBS feed. Even on the rare reruns it gets on the PBS Kids subchannel, it is still shown this way, even though said channel only exists in widescreen, leading to many completely unaware that the show was formatted this way to begin with. Mercifully, digital VOD versions of the show such as Amazon have the show in its original HD format preserved. The same is also true if you watch it on Netflix.