This isn't a direct answer to your question, but an experience of mine,
About four years ago I got involved in purchasing an airframe from DSA (Disposals Services Authority who dispose of equipment for the MoD) they were also involved with the mass selling off of equipment on the same site and were visiting in relation to that, which meant I got to meet them and ask some questions to some high up staff (who were very nice) within the agency - this wasn't long after the mass disposal of Jaguars.
From the conversation, it soon became apparent that the idea of all airframes/equipment beaing available for anyone to bid on is a false one, they are entitled to discharge items directly to their preferred bidders, and indeed was the preferred route.
This can mean that an airframe may go to a preferred contractor, rather than sell for less money to say a museum, or for more money to a private individual. When pushed on rare items that may still be in the system and up for disposal, it was actually quoted to me that if a Merlin engine was sold, it could as likely go for scrap than be sold to an individual.
The given reason behind this is simplicity, one scenerio is that an aircraft is actually just part of a larger lot of other equipment, the one preferred bidder is trusted to put in a price for the lot, and turn up on site and remove the whole lot.
The same is true for single airframes, the DSA knows the preffered bidder will come on to a station with the minimum of fuss, remove the airframe and go, where as unknown Joe Bloggs (who might have bid more) may come on to site with a Mondeo and a trailer, seeking local assisstance with disassembly and removal, and possibly leaving a mess behind.
So in simple terms, some airframes may never become publicaly available through DSA (or Edisposals), but be offered directly to the preferred contractor.
The item may never get a chance to be offered to a museum, or indeed the highest bidder.
How the choice to dipose of directly, or by open tender is made is unclear to me.
This was four years ago, things might be different now, but from my observations things are the same.