1630 is 'informational'. 1738 is 'standards track'. 1630 was intended
as 'this is the way it was', while 1738 is intended to be 'this is
what the standards group thinks it should be'. There's no mechanism to
officially 'obsolete' an 'informational' RFC, as far as I can tell.
Insofar as HTML is standards track, it should refer to standards track
documents.