The rights to Hitchhiker's and Shogun reverted to their credited authors (Douglas Adams and James Clavell) after they went out of print. The rest of the Infocom library was created as works for hire entirely by salaried Infocom employees, so the rights went from Infocom to Activision to Microsoft.

Right, which is why I assume the BBC has the entire rights today to Hitchhiker's and was gifted them by Douglas Adams' estate, but my searches didn't turn up enough evidence to back that assumption so I didn't include it, but I feel rather sure of it. (ETA: Related to the chain of how the BBC wound up owning was left of the H2G2 wiki for a time before spinning that back out to different owners.)