Dunno but the repo is 4+ years old.

> Maybe there's 3rd party code which SGI/HPE licensed?

IIRC, this was one of the complication of open sourcing Solaris back in the day.

An obvious source for 3rd party code is that it’s a real UNIX System V derivative, so the AT&T code would need to be cleared.

Even if there isn't any 3rd party code, the whole process of going through the codebase to confirm there really isn't any 3rd party code, and generally getting the legal department to sign off on it, is a lot of work in itself. My impression is that this kind of "historic source" release typically only happens if somebody sufficiently senior in the company cares enough to actively push it through. The default is that nobody does care that much, and it doesn't happen.

"Do nothing" has essentially zero downside for a big company that happens to have something of niche interest like this in its vaults.