Also, several characters from St. Elsewhere once appeared on Cheers, and since St. Elsewhere is just a figment of an autistic child's imagination, then Cheers, Frasier, The Tortellis, and Wings are also a figment of the child's imagination.
More likely, the St Elsewhere
characters are real people that appeared on Cheers
and also encountered the autistic boy at some point, thus leading to the autistic boy integrating them into his own fantasy life. Thus, Cheers, Frasier, The Tortellis, Wings,
AND Caroline in the City
(since Daphne & Niles from Frasier
once appeared in an episode of Caroline in the City
) are all "real." Their reality just happened to bleed into this child's fantasy.
Thankfully, that's a lot easier to "explain" than it would have been to explain the other Star Trek
shows had DS9
ended up as Benny Russell's fantasy.