Bad MARC Rant #1: Leader Positions 06 and 08

I understand why the MARC leader position 08 is a good idea in theory. In fact, MARBI Proposal 97-07 suggests:

a change in definition to Leader/08 code "a" for clarification; making code "t" (Manuscript language materials) obsolete in Leader/06 and using code "a" instead; redefinitions of codes "a" and "p" in Leader/06; renaming the 008 for Books to "Textual (Nonserial); and deleting field 006 for Mixed material.

I can safely say that some pretty funky stuff gets cataloged with the leader position 08 set as "a," and much of it is incorrect, at $MPOW and otherwise. What is Leader/08 actually supposed to be used for? MARBI Proposal 97-07 again states:

Code a indicates that the material is described according to archival descriptive rules, which focus on the contextual relationships between items and on their provenance rather than on bibliographic detail. The specific set of rules for description may be found in 040 $e. All forms of material can be controlled archivally.

Were that the case, why am I finding books cataloged using AACR2 with Leader/08 set to "a"? I'm also convinced that this extremely widespread by the information I can glean from the MARC Content Designation Utilization Project report, Format Content Designation Analysis: Data Report--General Profiles. Out of a data set containing more than 56,000,000 records, 0.3 percent have Leader/08 set to "a"; the breakdown by material type is even more interesting.

Leader/06 "t" was not made obsolete with arguably a good reason:

Leader/06 code t was not made obsolete and code a was not redefined because of concerns about how to identify material that is manuscript but not controlled archivally (i.e. not described according to archival rules, and thus not value "a" in Leader/08) if code t were to be made obsolete. LC should work with the archival and manuscript communities to bring back a proposal dealing with the remaining issues in the paper: making the three manuscript codes obsolete and finding a place to identify codex manuscripts.

This decision was made more than ten years ago and we still haven't made the manuscript codes obsolete. We also haven't found a method to identify codex manuscripts in MARC. In my mind, this in part boils down to the failure of AACR2 to define manuscripts properly:

4.0A. Scope

4.0A1. The rules in this chapter cover the description of manuscript (including typescript or printout) materials of all kinds, including manuscript books, dissertations, letters, speeches, etc., legal papers (including printed forms completed in manuscript), and collections of such manuscripts.

That's a pretty bleeping wide range if you ask me. One can obviously see that the proliferation of standards that followed were designed to fill this gaping hole that JSC left in AACR2. RDA only has one element that references manuscripts at all ("Production method for manuscripts"), so who knows what direction that'll go. Luckily, RBMS has been working hard on all of the DCRM standards!