I just realized that when Han rescues Luke during the trench run scene by shooting one of the TIE-fighters and knocking Vader out of the way, that we only see Han in close-up and then suddenly Chewie is in the co-pilot seat after the DS explodes. Since obviously someone would have had to be operating the laser cannons, and there’s no one else available but Chewie, I wonder if they cut to the CU to avoid any continuity errors as Chewie is suddenly back in the cockpit shortly after. Looking at the scene now it really seems like Chewie was always sitting next to Han and they had to cut around it.
The Millenium Falcon has more weapon systems than just 2 quad laser cannons:
^Read label #50 and the armament subheading in the blue box.