71 minute version?

Probably a "TV version." Allied Artists packaged a bunch of Corman films (including several of his independent Filmgroup releases, as well as movies he made for Allied Artists) in the late '60s, I think it was, for TV syndication, but a lot of the stations wouldn't sign on at first because the movies were too short. In those days, TV stations didn't think their audiences would put up with a 67-minute movie padded out with 23 minutes of commercials in a 90-minute time slot. Imagine! [Nowadays, we get TV broadcasts in America with a minimum of 22 minutes of commercial time in a SIXTY minute time slot!!!]

So, Corman had most of them "augmented" -- years after they were made -- with new scenes to pad out their running length for television. Corman didn't film any of these new scenes himself (at least, not officially). They were mostly shot by Monte Hellman and Jack Hill, from what I've read.

I never heard of this being done to Not of This Earth, specifically, but it was done most definitely to Creature from the Haunted Sea, The Last Woman on Earth, Attack of the Giant Leeches, The Wasp Woman and some others. You can find both the original and longer TV versions of almost all of these movies in different VHS and DVD releases.

I have the 67-minute version of Not of This Earth -- it's the only one I've ever seen, at least since I was a kid -- so I'd love to see the longer version some day, just to see what was added to it.

I had discovered I had 2 versions of this movie, One of 64 minutes, the other 71. The quality on the 71 minute film was terrible compared to the original 64 minute one. From Wikipedia:

Production notes

The film was released in the USA on the bottom half of a programmed double bill with Attack of the Crab Monsters.[1][2]

Some releases ran 71 minutes. These copies did not include extra material; instead, the distributor edited certain footage twice into the film, for instance a dialogue between Johnson and a representative from Davanna, which appears as a pre-title sequence and again some minutes later into the film. This version circulated on US TV stations, 16 mm copies and on bootleg DVDs and videotapes.