There are photos of Warshaw being handed the first cartridge pulled out of the ground.
One of the reasons why this stayed in the "rumor" category for so long was because Howard Scott Warshaw claimed several times that he had never heard of the unsold or returned games being dumped in the landfill. I've read that from him in a couple of articles throughout the years. So that helped take it from hazily remembered fact to vague internet rumor over the course of 30 years.
That copy of Centipede they retrieved looks like it was stored in one of those plastic cases that shops like Target used to put games in so they could be hung from pegs. I've only got one or two of those, I always wished I had more.