Hey Rod, I'd also wondered about that part from the Karl too, but never checked to see if it's right. Well, I just dug it out & placed it on the Panther part & also checked my ref & I'm positive it's from this kit. It is a match IMO.
I don't know either with the notion this kit wasn't around in the ANH era. I can't confirm for certain either way. The only thing I can think of was the B/W photos were taken quite a while after ANH, but before 'Empire'. The Karl part could have been added during this period & not being an 'original part. This would explain a few of the other missing parts that show up in these 'early' B/W photo's, such as one possibly from the 312b on the starboard side mandible wall.
IMO, the Falcon got pretty beat up in storage between ANH & Empire so new parts were added & somewhere during this period the B/W were taken.