CAA couldn't answer me. Or at least the person on the phone was clueless!
I did my ME-IR skills test in 2008 and when I asked to have an IMC rating added on the back of my IR, the CAA said "you don't need it." I wasn't up for a fight that day so left it.
When I did my CPL in 2009 I insisted an IMC being added to my newly issued CPL (and I knew that one new rating could be added for free). They agreed. I had already done my first ME-IR reval in the sim by the time I headed off to Gatwick so my IMC rating was valid to November 2011. Dates entered by the CAA.
Therefore the examiner each year has simply extended my IMC rating every time he does my ME-IR renewal/reval. Simples.
BTW: the cross crediting flow chart in Appendix 3 of Standard Doc 14v6 is rather strange as you cannot progress down the flow chart if you haven't got a valid SPA IR. I thought the whole aim of the cross crediting is to allow credits from MPA IR to SPA IR. Unless there is this bloody confusion again and what they actually mean by valid is previously held. Who knows..
Edited to add: If my above interpretation of the terminology is true, then it also means that a previously held SPA IR is satisfactory to enter a first MPA Type rating course.
ah well ...