Lab, Welcome!! Good sleuthing there.
So yes, it does appear B was indeed there around the time of filming. SW Chronicles shows these two B&W pics that seem to be taken during ANH filming, and B is indeed there, in some other same time/era pics, it is definitely gone. So, as it goes with us builders, you have to make concessions and decisions of what you want to put down. If you want to be ACCURATE, you would be correct having it in place, and not having it in place
. As for A, all the known evidence shows it was always broken.
For my build, because I agree the little shadow is evidence the whole part was there and got broken right around filming time, I chose to put the entire part on mine, as I like the 'balance' to both sides. Hope this helps a bit.
(EDIT - Lab, you've caused me to think this through a bit more, and after re-watching the TIEs attacking the Falcon after they leave the Death Star, and consistent with the Edlund Blue Screen photo - I've now decided I will remove the B part on that side, and chop up the strut!! I love this kind of feedback to get you re-thinking things, thanks!!)