You got me all excited wxgill. I used to collect stamps (yes, geeky, I know) and thought for the first time ever I might have some idea about your topic and be able to help.
Collected every issue of QE2 stamps, mint, franked and first day covers. Finally gave up about 10 years ago as they took the piss bringing out fresh issues every few weeks to milk mugs like me. Originally they only brought out new issues for really special occasions, ie years apart. Interestingly it was Tony Benn as Postmaster General in the early sixties who came up with the money making idea.
There, I feel better now even though nobody wanted to know this information.