Hey, It's That Guy!: In the original Los Angeles-based episodes of Mathnet, the chief, Thad Green, was played by James Earl Jones. Despite a change in chiefs with the move to New York City, Jones made one appearance via phone in a season 4 episode.
This also applied to people working off camera. First- and second-season writer David Yazbek later co-wrote the theme songs to Where In The World Is Carmen Sandiego? and Where In Time Is Carmen Sandiego?. Pat Tuesday and George Frankly even appeared in a first-season episode of the former, in which they gave out clues to the gumshoes to where the crook had gone.
Jim Thurman as Glitch in the Mathman segments and as supporting characters in the Dirk Niblick segments.
Keep Circulating the Tapes: The series has not been rerun since the early 2000s, when it was rerun on Noggin, and there are currently no DVD releases planned. Domestic recordings do exist of many episodes, and they sometimes show up on YouTube, but they are nowhere near exhaustive, and quality varies widely.