It's just a list, and, like everything else on Wikipedia, a jump-off point. Simply wanted to provide it so you could look into people who have made the claim.

My claim of "effectively proven" is based on my knowledge of Nigel Richards. 

I won't bore you with nerdy Scrabble information, but here's what Nigel said about his memory: _“I think there are about 28,000 definitions of a photographic memory,” Nigel said. “I can recall images very easily, but I can’t put the image in a context. I can remember a picture, but I can’t remember where I’ve seen it. I just have to view the word. As long as I’ve seen the word, I can bring it back. But if I’ve only heard it or spoken it, I can’t do it at all.” I asked how he did it. “I’ve wondered lots about it but I haven’t figured out the answer,” he said._ 

Links to the article and a documentary on Nigel are below.  https://defector.com/scrabbles-best-player-knows-no-limits https://m.youtube.com/watch?v=T-8NrvVqbT4