My shorter OED contains 163,000 words (compared to the 600,000 words of the longer).
According to this site I know 71,000 words... Let's test that against the OED. I should have about 43% chance if knowing a word picked at random.
In my totally scientific test (ha) I chose 50 words at random from the OED and discovered I knew 29 of them for a score of 58% which is more than two sigma from 43%, this disproving the hypothesis.
I forgot what that was now, but it was a fun experiment.