It's probably hard to prove with something from 1981 but no license or copyright doesn't mean the source is open for taking. It basically means you just haven't set a license and could do that at any time, rugpulling the code from anyone who uses it. This is why projects like Fedora and Debian make sure everything they ship has a license.
me-vs-cat|6 months ago
Are you sure? That's before the US joined the Berne Convention, and also not long after the Computer Software Copyright Act of 1980.