A newly unearthed Aztec tomb must have been created after 14

Dear goodyear2013,
I"m happy to respond.

First of all, as you may know, one of the best tests for a good assumption is the Negation Test, discussed here:
https://magoosh.com/gmat/2013/assumption ... -the-gmat/

I have some doubts about this particular question. The set-up doesn't seem realistic. I don't know that we have such precise data on Aztec styles and practices in the middle of the 15th century. The prompt scenario strikes me as highly contrived, to the point that some who is an expert on the Aztec might laugh at it. Many of the GMAT CR questions have a far more realistic feel to them.

Nevertheless, here's an analysis of the answer choices:
Which of the following is an assumption on which the argument depends?
(A) The style in which the Aztecs built tombs did not change between 1428 and 1430.
Even if the style changed, it's not clear this would change either the wood they used or the headdresses they put inside. The relevance of this to the argument is not clear. This is incorrect.

(B) There is no other evidence in the tomb that can be tested accurately for age.
Maybe there is some other evidence that just wasn't mentioned. Maybe that other evidence would strengthen the argument even further. We don't know. This is incorrect.

(C) No stocks of the old wood existed after 1430.
This is a niggling one. If no stocks of the old wood existed after 1430, that would strengthen the argument. But a strengthener is different from an assumption. Suppose we negate this and say: plenty of stocks of old wood remained after 1430. Technically, the argument says, "It also could not have been built after 1430 because it contains a type of wood that the Aztecs were known to have stopped using in that same year." So, even if they had the wood available in stockrooms, they stopped using the wood in that year. Because of this, we have to say this answer choice is incorrect. First of all, this is unsatisfying because it's a real picayune semantic distinction, and more important, it's 100% unrealistic to the situation --- if the Aztecs had leftover supplies of a certain kind of wood, why on Earth would they stop using it? I can tell the question author intended this to be a wrong answer, but it's not a satisfying wrong answer.

(D) The Aztecs did not construct the tomb over the course of many years.
This is the intended correct answer. If we negate it, and the tomb construction took, say, 20 years, then it very easily could have both the wood and the headdress and still not have a construction located just in that narrow window. Thus, if we negate this, it obliterates the conclusion of the argument. That's the sign of an assumption.

(E) The headdress was familiar to most Aztecs in 1428
It doesn't matter how familiar the headdress was to most Aztecs. Perhaps it was only know to the secret society of priests who presided over the burials. How familiar or popular it was is irrelevant. This is incorrect.

Here's a much higher quality CR assumption question, for practice:
https://gmat.magoosh.com/questions/3137

Does all this make sense?
Mike