Having now listened to Ashley Vallier's testimony in full, I respectfully suggest that is not the significance of her testimony. And it's not a significance that KR's own defense attempted to draw out on cross examination.
What AV said is that there were a number of pieces of which she could not make a successful fit in her "jigsaw puzzle" exercise. Given the shattered condition of the tail light, that is not surprising. AV mentioned that a number of pieces were so small as to make any attempt at puzzle-fitting a non-starter. And, even with respect to the somewhat larger pieces, it's plausible (even inevitable) that some of these pieces will lack a suitable connection, given that some portion of the tail light is shattered to bits and other portions likely missing.
It is entirely consistent with AV's testimony that all of the pieces submitted to her came from KR's tail light. On cross, Yanetti's only questions directed at the "jigsaw puzzle" exercise sought to point out that there was a significant section missing. He did not attempt to suggest that the non-puzzle-fitting pieces did not come from KR's vehicle.