I just got an e-mail from a very bright guy who for reasons unknown to me is reluctant to post in AWADtalk.
I am posting it because I think it has valuable information. I hope he will not resent my doing so without asking his permission.

William Dwight Whitney, The Life And Growth Of Language:

...but thirty thousand is a very large estimate for the number [of words] ever used in writing or speaking, by a well-educated
man; three to five thousand, it has been carefully estimated, cover the ordinary needs of cultivated intercourse; and the number
acquired by persons of lowest training and narrowest information is considerably less than this...

I'd suggest that the capabilities of a "well-educated" man of 1875 were roughly equivalent to those of a "well-educated" man of
2002 regardless of how much the number of available words to learn has changed or not changed. I'd further suggest that the
educational authorities have found ways, over the last several decades, to exaggerate, especially to inflate, just about every
statistic they've ever provided, i.e. of troy's treatment.

Whitney was a Professor of Sanskrit and Comparative Philology, Yale College.