At the moment there has been no transfer of rights in the early
RFCs to the IETF Trust, so I think you need to ask the
RFC Editor, or simply look at
IANAL, but I have been told that in any case it is necessary
to check with the original authors.
I am getting the strong impression that nobody really knows the answer.
Since RFCs have been reprinted all over the place without permission over
the past three decades, and there's a fairly strong presumption in law
that you can't revoke permission that's already been given, I've told him
that at least for the early RFCs with no copyright notice or claims, he
can go ahead and use them.
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