They were all set in the same universe. At least it would appear that way if you take into account one specific character: Detective John Munch, played by Richard Belzer.
You might recognise him as this guy.
The man not the pooch.
Look familiar? That’s probably because over a period of around 20 years he appeared in a total of 453 different episodes, in 10 different television shows.
Yup, that’s right, 10 DIFFERENT TELEVISION SHOWS. Which therefore means that Munch is either TV’s biggest in-joke or he’s the character glue that holds it all together, proving once and for all all of the above TV shows belong in the same universe.
Which is astonishing. It also opens up some interesting theories about Sesame Street, what with it appearing in the exact same world as The X-Files. Could the infamous puppet show actually be set in a far of alien world or third dimension? Only Detective John Munch will ever really know for sure.
Here’s Richard Belzer himself explaining the whole thing. Sort of.
Here's all of the shows that he's popped up in so far:
Homicide: Life On The Street
Law & Order: Special Victims Unit
Law & Order
The X Files
Jimmy Kimmel Live!