As you will see, these are matching strips, the stamps being numbered 91-96 in both strips, from sessions 635 (Machin) and 616 (Flag). Because Richard was buying in quantity and as Collectors Strips (ie multiples of 6) I didn't realise then what I deduced when I received my own stamps from the organisers.
I was interested to note that the single receipt showed the purchase of both types of stamp:
Reel B, leading me to the inevitable conclusion that the machine had, as well as a reel dispensing Post and Go Labels (for immediate posting), two rolls of Faststamps.
Examination of the stamps shows that they have follow-on numbers in the same session.
My Flag stamps are numbered 01-18 and the Machins 19-36. I don't think any of the eBay sellers has, in the same lot, listed different stamps with the same session number. I don't think it had been mentioned anywhere else until I asked around, and Brian has now provided full details on his postagelabels.uk blog.
Writing about the situation at Stampex, where the machines were used before being taken to Perth, Brian shows a picture of the inside of the machine:
In his report, Brian lists which labels were used in which self-service machines at Stampex on each of the days. For example:
Fri 28 Sept
C & F
C = Cattle, F = Flag, F-DJ = Diamond Jubilee overprint on flag.
I wonder how many people actually bought different stamps with the same session number at Stampex? Probably few. Certainly I've not seen any sold with that mentioned.
As an identifier it is of little consequence as the new format of the coding on the Version 2 machines is sufficient. But when these are introduced into Post Office branches to replace the Wincor-Nixdorf machines, it will present additional opportunities for Post Office to offer a wider range of labels, either pictorial/non-pictorial or maybe normal and 2nd class as currently 2nd class is only a 'Post Now' option on Post and Go machines.
We now have no stock of the Perth overprints.