OK, my bad: The oldest RFC is just "experimental" while the newer ones are "informational", and explicitly stating "It does not specify an Internet standard of any kind."
No wonder its not standardised, considering that almost any server out there uses a different, partly incompatible set of extensions (for server-to-server communication, at least), depending on which servers it was forked from (very few are not in some way derived from the original ircd[0]).
