Going by memory only and subject to correction, first couple of hundred matched sets were marked with a "B" prefix (as if they were an open edition) by accident, that was corrected and the rest of the matched sets were continued with either an "A" prefix or with no prefix (like a limited edition) but there were a certain number of matched number sets with the postal stamps included and then after that they were no longer sold as matched sets

I do not remember how the rest of the matched run was numbered, was it with an "A" prefix or just a number ?

I have a matched set #B204