No reasons given to think it actually did (Score 3, Informative)

What seems to happen here is that a person uploads a movie to Archive claiming that it's public domain and Archive does whatever research they do and decide whether to distribute it.

Another post points out that the Copyright Office database says Plan 9 was registered in 1958 and renewed in 1986, so the reasonable assumption would be that it's still covered unless the owner places it in Public Domain.

Archive's page for the movie says the uploader's site is at www.k-otic.com, a site which is basically an uploader's blog which does claim to have uploaded it.

The person who uploaded it doesn't seem to really do any research on movies' copyright status before uploading; (s)he says in a post about another upload that:

"the problem is that there is no really reliable source list/search engine on the internet where you can go and find out
but the people at the internet archive check all uploads and when they say it`s ok ... it`s ok"

This does not really lead me to believe that the uploader contacted whoever owns the rights to Plan 9 and arranged for the film to be placed in the public domain. ;-)

Summary: there's no reason to believe Plan 9 actually is Public Domain, since the first person to make the claim (the uploader) admits that (s)he has no way to be sure about the status of the movies (s)he uploads and Archive gives no evidence to support the claim except the uploader's original assertion.

-robin