The problem that Dublinpilot has come across stems from the fact that the CAA while only publishing a single chart edition each year, they make several reprints during the year and each reprint can include many of the hand amendments published.
For example, an obstacle may be missing from the 1st print of edition x. An amendment will be published on the web. When the 2nd print is made, that obstacle may be added to the chart.
Thus while there is a single edition, there can be several versions of that edition in use at any time. The amendments have to cater for the worst case.
You better be very sure of this, DFC, because I have personally never seen a CAA 1:500k chart of a particular edition (say Edition 30) with a date on it other than the very earliest one.
Could simply be that shops order what they think will be a fair chunk of their annual sales and then aim to sell out old stock first...