One flaw I've always found in the world of crossovers is the Tommy Westphall universe, while true it's most likely the most expansive universe in fiction, I do think it's size is exaggerated as people count cigarettes, shared brands and such as clear connections.
The thing about the Tommy Westphall universe is that due to everything connecting to St. Elsewhere which was SPOILERS!!!!!!! all a dream in the mind of Tommy Westphall, some of the logical inconsistencies can be overlooked such as Friends characters watching Cheers despite Cheers being in the same universe. Dreams often don't have consistent logic.