Back in the day, the covers were often finished before the books were. I confess I've been known to adjust the books to make them fit the covers. (Beverly saves the day in Dragon's Honor
because I'd seen the cover art and knew Gates McFadden was going to be on it . . . .)
"Hey, Greg. Is there a helicopter in The Eugenics Wars
"Er, not yet."
there be a helicopter in the book? Because we put one of the cover."
"Fine. I'm sure I can work a helicopter in somewhere . . . . "
(This is also the reason Iceman suddenly shows up halfway through my X-MEN trilogy. Because he accidentally ended up on the cover!)