I meant meeting exactly prior to WWE. That I believe IS a retcon...
They wouldn't necessarily have to meet for the storyline to work. Things Sinclair would be doing could effect what Sheridan was dealing with and vice-versa. Much like how it was in the second season with Sinclair, the Rangers, and Sheridan.
But it would be cool if they did meet, even if it is a retcon. Although, it be a better story, imo, if they didn't.
And some of the material in B5 season 5 was stuff he'd originally planned to do in Crusade, I believe.
Not necessarily
Crusade, but from some of his earliest ideas on a spin-off. After the fourth season, he proposed a series about Sheridan, Delenn, some of the rest, and the Rangers building the Interstellar Alliance. IIRC, it would've had them traveling to the different worlds in the B5 universe.
Then season five got green-lit, and he had to come up with another spin-off. Also, iirc, TNT wanted the spin-off not to feature the original cast.
JMS earliest notes for a spin-off go back to the pilot and first season of B5. In a
Cinefantastique interview, he stated that there was one idea that could be spun off of the five-year story and that once he told that he'd probably "have said everything he wanted to" in television. (I'd quote the magazine but it's in storage in San Diego.)
Of course, from his "Sinclair" outline of the
Babylon 5 story that spin-off would've followed Sinclair, Delenn, and their son on the stolen
Babylon 4 dealing with the Shadows (not the Drakh) run amuck and Londo's reign as a puppet Emperor, eventually building something like the Interstellar Alliance in the process.
So I think some of season 5 took that empire building arc from the two ideas he had for those two spin-offs. Although, he probably would've used them as well in
Crusade.
I'm sure
Jan can speak with more authority on the subject.