I've had much the same experience, although I can't say it was with the "top names in numismatics." I even once casually mentioned there was an entire set of overstrikes for sale on eBay at a show one day and saw they'd been sold by the next morning.... I don't know who bought them, but I have suspicions.
A "1964-D" Peace Dollar is a "fantasy date" because the US Treasury has officially stated that none were issued, all were melted, and none exist.
A few people are rather lucky that's all they have been. As I said, given the means and reasons to do so, I wouldn't be so nice.
Has PCGS paid out on its reward yet? No. Therefore, the reward is no evidence of the coins' existence. Has one of the coins surfaced in any form outside the US Mint in the last 50+ years? No, not that anybody will admit to. Therefore, the mere possibility that one "could" have gotten out is not evidence of their existence. Do US Mint records indicate that any of the coins still exist? Why, no they do not! This is evidence that the coins do not, in fact, exist. Given this, claiming the coins exist is an extraordinary claim, and, as such, requires extraordinary evidence, like an authenticated, original piece.
So you're telling us a fantasy-date 1908 Lincoln cent struck over a 1909 Lincoln cent isn't a fake cent?
This is very interesting, because I seen the real deal about 10 years ago at a local show, or so they said ...