Explanation

The blank structure for this problem is tricky; in such cases you need to pay attention to the specific words in the sentence that give hints to the meanings of the blanks.

For the first blank, you are looking for a modifier to “comprehension.” This “comprehension,” you learn, is impeded… by labyrinthine
complexities. In other words, total, or exhaustive, comprehension is difficult because of these complexities.

For the second blank, the key word is “reliable.” The relation of this word to the blank is given by “even the most,” telling you that these vintages are subject to something opposite to “reliable” — that is, remarkable variance.

An exhaustive, remarkable variance.
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Sandy
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