Let's approach this from a different direction. Given there is general acceptance that we will never be able to produce a volume that suits everyone, why not aim for a really basic volume on cheap loo-roll paper (as per Coincraft catalogues) that everyone and their dog can afford? I think that people are getting too hung up on varieties that are already too complex for many novices or would be collectors. Variety collecting is a bit like an Alice in Wonderland story where nothing is as it seems and requires a bit more than a quick look through a keyhole. A basic volume would cover every type with a life-size coin identifier, or at least a generic indicator for design and size. Milled coinage usually being done on reducing apparatus means that you can just show the basic designs with the diameters listed. All years would be included priced to the cheapest as per Spink now, with a note that varieties exist denoted by a mark of some form, the exact mark indicating which specialised reference contains the required information. Essentially it would be an overview of the contents of in-depth volumes of a given denomination or series. In reply to David's post above I can see the case for including the undated mule as it would be no different to a year change that is in regular currency and known to the public, but the 2p mule is not common knowledge to the public, nor are they encountered on a regular basis.