The IESG announced on 2005-02-24 that it had approved the document "The 'tag' URI scheme" as an Informational RFC. IANA registration followed soon afterwards. The RFC wasn't published until 2005-10-26. A couple of months of that delay was due to the authors' attempt to upgrade the syntax to accommodate RFC 2822 email addresses, during the 'authors 48 hours' :-).
The final (7th) draft prior to RFC status is available in html and txt. We used xml2rfc to produce them from XML.
Changes from 06 to 07 following the IESG discussion in December: Updated the draft to remove tag IRIs (Internationalized Resource Identifiers) -- the IRI material had problems and seemed best left to another day. Stopped line wrap on syntax specification. Added IANA Considerations section to request URI registration.
Changes from 05 to 06: Updated the draft to specify tag IRIs (Internationalized Resource Identifiers). Fixed syntactic bug -- we used "4*DIGIT", "2*DIGIT" in the date syntax when those should have been "4DIGIT", "2DIGIT". Made a few syntactic simplifications. Added some text to state that all tag minting authorities should use record-keeping. Pointed out that tag namespaces can be delegated to groups or individuals within an organisation. Made a few improvements to the text.
Changes from 04 to 05: Clarified that dates must be reckoned from UTC (not the tagging entity's local timezone). Removed the URN namespace application. Restructured and tidied the document to make it clearer.
Changes from 03 to 04: (not sure right now)
Changes from 02 to 03: (not sure right now; probably something in whole-year syntax)
Changes from 01 to 02: no changes in intent; editorial changes: fix some ABNF errors, and better explain the property of being single-valued.
Changed from 00 to 01: drop "t" dates, drop why-not-URN, add URN Namespace ID application.
Changes from 2001-05-30 to 00: allow long-form dates and require short dates to be prefix by a "t" to prevent ambiguity in 2000 years.
Draft of 2001-05-30 (early version of 00): plain text or PDF. Changes: make delimiter between authority-name and date be a comma (instead of a slash, which violates RFC 2396).
Draft of 2001-04-26 (earlier version of 00): plain text, PDF, or PostScript.