Does everyone know the definition of the word "basically"?
Does everyone know the definition of the word "pilot"? It does not just mean 'first episode'. It's the the episode or movie used to show TV execs in order to *sell* the project. That it's often used as an introductory episode when the show is aired doesn't change that essential component.
"The Gathering" was a pilot for B5 and the cast and station geography went through substantial changes between that airing and the show being put to shoot. Star Trek had two pilots which were later used as (or in) episodes of the approved project.
"A Call To Arms" wasn't a pilot or even a backdoor pilot, it was a bridge between the two series. As JMS said in his Premise for the then-called "Eve of Destruction":
"The Eve of Destruction" would serve as a link between the two series, but at the same time allow for a clean segue from one into the other as independent entities. A moment of transition which TNT can promote from both sides.
ETA:
Guy Gardner is correct that the trilogies are hard to find for a decent price. However, I've got copies and I'm willing to lend them to folks here for the price of postage both ways. PM me if interested.
Jan