Is it clear that The Open Group or IEEE actually have a clear right to claim copyright of the POSIX api given this ruling? Were they assigned or licensed that c

Is it clear that The Open Group or IEEE actually have a clear right to claim copyright of the POSIX api given this ruling? Were they assigned or licensed that copyright by AT&T or any of its successors? It seems likely enough that in the 80s this was not seen as necessary, and the old guard of UNIX implementers were still being quite belligerent towards each other at the time, afaik.