The RFC series has long been THE archival series for the Internet. To
avoid Internet Drafts becoming another archival series, thus creating
great confusion, the IETF has chosen to make Internet Draft ephemeral,
timing out after 6 months. Indeed, that is why they are called
DRAFTS.
The intent is that when good & useful information and ideas are
published in Internet Drafts, they should become Informational RFCs if
they merit preservation and referencing.
A Working Group sometimes accumulates a froth of subsidiary drafts with
information that is worth preserving, but ancilliary to the primary
standards-track work of the group. The chairs should take steps to
turn these into Informational RFCs. This was the case for the RSVP
working group, for example; I know of at least once such "left-over"
I-D that should have been published as Informational. It did not
happen because the working group chairs were tired; however, it was
their failure in this case. I expect that similar cases exist in other
working groups.
Bob Braden