It looks to me like the original first comment about the NYT article has now vanished. It may have been deleted. From what I can vaguely remember of the comment (when this thread was first posted) it picked up on the following paragraph in the article:
"Researchers said they were baffled by the magnitude of the drop. Some cautioned that the results could be overstated because Americans without a high school diploma — about 12 percent of the population, down from about 22 percent in 1990, according to the Census Bureau — were a shrinking group that was now more likely to be disadvantaged in ways besides education, compared with past generations."
So the proportion of Americans without a high school diploma has nearly halved from about twenty years ago, compromising to a significant extent the idea that this is a like-for-like comparison.