So we've all seen now that
PokemonLetsGoEevee.com and
PokemonLetsGoPikachu.com have been registered by CSC. CSC is a company that files domains for other companies and you just first show proof and file appropriate paperwork to obtain a domain through them. It's difficult, but not impossible for a random person to claim these domains. It would also have to be someone who is familiar with these leaks and that's a pretty small amount of people.
That being said, most of TPCI/Nintendo's domains have information in the WHOIS that explicitly says 'Nintendo.' These two, however, do not. Yes, this is evidence towards someone not affiliated with Nintendo snatching the domains, but Nintendo has in the past acquired anonymous domains through CSC that were never explicitly tied to them, but turned out to be theirs. An example of this is
pokemondeltaemerald.com. This website was registered by CSC but never said Nintendo in the WHOIS. The site, however, does direct to the official Pokemon website so it is undoubtedly their domain.
All in all, this doesn't prove anything nor does it disprove anything. It does seem like, however, that more domains are being taken down which wouldn't really make any sense unless Nintendo was looking to acquire them which they can do with a cease and desist/copyright claim. In my personal opinion, I think all this information supports the Let's Go games being legit, because there are just too many coincidences and especially with E3 coming up, where we almost certainly will hear something, it's very likely we will get a little teaser before.