[rfc-i] "obsoleted by" in RFC 5143

[Julian Reschke]

Hi,

<http://tools.ietf.org/html/draft-iab-streams-headers-boilerplates-08#section-3.1> 
points out:

       ...Currently two
       relationships are defined: "Updates", and "Obsoletes" [RFC2223].
       Variants like "Obsoleted by" are also used (e.g in [RFC5143]).
       Other types of relationships may be defined by the RFC Editor and
       may appear in future RFCs.

That confused me a lot, because "obsoleted by" is the inverse of 
"obsoletes", not a variant, right?

But, indeed, RFC 5143 *is* obsoleted by RFC 4842, which was published 
one year earlier.

Does anybody know what exactly happened here?

BR, Julian