A novelização oficial de Alexander Freed explica isso. Eles provavelmente estavam na última onda de transportes levantando Yavin
{{ Mon Mothma discussing Admiral Raddus}}
“He’s left already.” The man was almost stammering. “He’s in orbit aboard the Profundity. He’s gone to fight.”
Note que ele simplesmente deixou Yavin, e ainda estava em Orbit, reunindo as forças lá no momento
“I see,” she said, and slowly smiled. ...
Less than ten minutes later, sirens were announcing the departure of Red, Blue, Green, and Gold Squadrons along with the U-wing transports. Raddus had already contacted all capital ships within range of Yavin or Scarif. ...
E enquanto os últimos transportes estão sendo preenchidos, ela vê R2-D2 e C-3PO indo em direção ao asfalto , o que significa para aqueles transportes sendo preenchidos:
... As the last transports began to fill, she turned back to the corridors of the ziggurat and set out for the communications center. She had to step aside for a gold-plated protocol droid and an astromech unit hurrying toward the tarmac, and faintly overheard the former indignantly declare:
“Scarif? They’re going to Scarif? Why does nobody ever tell me anything, Artoo…?”
(Chapter 17)