Joe is a pal of mine who lives a few doors away. We were discussing Machins last night (as well as other things).
The topic got round to overprinted Boots miniature sheets and Joe informed me that he has one of the unbranded sheets (without the Boots logo) with blue phosphor that was issued to mark the 40th Machin anniversary.I had not heard or seen this variety so I asked Joe to dig it out for to look at.
It turns out that it was issued in 2007 at JAPEX - TOKIO as a Publicity Overprint which also commemorated 40 years of Machins 1967-2007. A limited edition of 500 were prepared as a special exhibit by the British Stamp Study Group of JPS. Well I live and learn.
Today I actually found one on the net for sale at £9.99, I'm not sure I admire it that much to pay this price, but have copied the image for you to look at.
News is also out with the codes on the Arnold Machin Centenary Souvenir Sheet. It has been confirmed that this has the year code AM11 and the source code MMIL.