Even though Gable is seen in uniform when Lombard's plane crashes, he didn't actually enlist in Army Air Force until six months after her death.
When Gable drives onto the Paramount lot to talk to Lombard about starring in "No Man Of Her Own" (released in 1932), a billboard outside her dressing room advertises "The Princess Comes Across" - a Lombard picture not produced until four years later.
Hedda Hopper approaches Gable at a party while Gone With The Wind is in production and, after making a reference to co-star Vivien Leigh, makes Gable promise she'll be invited to watch filming of burning of Atlanta. In reality, burning of Atlanta was first scene of GWTW to be shot and Leigh wasn't even cast at that time.