As always, many thanks sbm12.

I looked at a few (actually, many) CO flights during 2011~2012 and couldn't any difference in the number of seats allocated to the non-elite vs elite buckets for prem class travel, either free or award. i.e.,

ON = O avail
IN = I avail
RN = R avail

Hope that they actually do allocate more seats to the xN buckets. (Am assuming that the xN buckets are actually sub-buckets (ie, if a 1k pax books into an xN bucket, then both the xN and the x bucket decreases by one).