If this helps anyone: I'm not thinking of NA questions as "which one of these ACs is necessary for the argument to work logically"-- instead I'm thinking of them as "which one of these ACs, if not true, would destroy the argument" or "which one of these ACs does the author have to agree with."

#feedback I think you're missing what makes C a tempting answer choice. Yes, the present archaeologists already possess all the information about the mosaics, making the information offered by leaving them in their original position irrelevant to them. However, the stimulus discusses future archaeologists who a) might not have access to the records of the present archaeologists (i.e. all the information such as the material of the mosaics) and b) won't have access to the mosaics in their original location because they have already been removed. SO, C tempts us because it is saying that if the mosaics were left in their original location, future archaeologists might have had access to more information about them otherwise inaccessible had they been moved.

I understand what makes A the better AC, but C is more tempting of an answer choice than addressed in the explanation and I think it is worth covering in more detail.

#feedback So unhelpful to get to a wrong AC and only say "this is just not right." This is called an explanation video, meant to explain why the right ACs are right and why the wrong ones are wrong. I understand you have to make a lot of these videos and go through a ton of questions, but it's very frustrating to want to know why something is wrong only to be met with "because it is."