It is not much but it is certainly interesting that there appears to be a difference in the orientation of the rearview mirror between Altgens #6 and Altgens #7.
The four identical horizontal lines on Altgens 6 show that the car and the mirror are horizontally aligned:
It is a bit more difficult to find the car horizontal in Altgens 7 because the car is accelerating as it negotiates the left to right curve and Clint Hill has jumped on the left rear. Both of these things push the car down toward the left rear.
But it does seem that there is a marked difference between the orientation of the mirror between Altgens 6 and Altgens 7
The AR15 hollow-point that dented the chrome trim at say Z310 contacted the chrome on the crease in the chrome, a little right of center of windshield.
Below the chrome crease the chrome angled forward a little.
The radiating initial lead splatter of the disintegrating slug thusly angled down, & forward a little, & some of the initial splatter hit the right-hand-side of the mirror, knocking that side down a little (& damaging the mirror they say).
Bearing in mind that the rhs of the mirror would have been turned back a little compared to the lhs. Thusly the rhs suffered splatter, the lhs suffered zero splatter.
Halfway throo impact the dent would have been deeper & the splatter would have been more evenly spread all round (up down left right) at 360 deg, & all of it backward, ie not near the mirror.
I have never seen an exact description of the damage to the mirror. I doubt that damage is visible in photos at Parkland & at the garage.
I am fairly certain that the mirror is not listed as needing replacement during the Dec1963 repairs & upgrades & modifications to the jfklimo.