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Hi Nick
I understand the confusion: the one you refer to with the blue ground is indeed an Aladdin's Cave design by Perthshire - but it is the version they released in 2002, called 'Cave'. Because it was released in the year they closed it is quite uncommon, compared to the PP7. 'Cave' may have had a PP number, but I don't think it is recorded anywhere; they released a PP248 that year, so I guess it would be around PP250 or thereabouts.
You have probably noted that the Perthshire book only goes up to PP185 in 1997: there are a good number of PP designs ( more than 60) that exist from 1997 to 2002, and which turn up from time to time. These can really puzzle collectors - not to mention all the one-offs, trial pieces, and variants which exist too! I have managed to get copies of most of the catalogues or product lists from the period 1998 to 2002, but I am not sure that the full list for 1997 (including mid year) is available.
Alan