Yes, it does seem complicated ... because it was!
From The Complete Guide to Perthshire Paperweights
, page 75:
COLOR VARIATIONS: Ground and cane colors vary unless a specific color is indicated. Different cane colors can cause major differences in the appearance of the weight by accenting different parts of the design.
My understanding is that an Edition applied to the Design (i.e. "PP" or other Designation number).
There seemed to be "Limited Editions" that had no edition number specified. Annual Collection, Christmas and Special Editions did have numbers but again colours could vary. An example of further confusion is the Annual Collection "1972B" weight which was the same design as the "1971D" except that it was faceted.
I would add that in some cases, weights can have a slight difference in the pattern even though they have the same design number!
A specific example of the different colouring and also partail design appearance is highlighted by such as PP12, whch is designated as a Limited Edition. For 1969 to 1975 the base colour was translucent with white lace and for 1976/7 they had a coloured lace ground. Also, the base colours were varied as blue or light green, although for 76/7 they were just blue.
And PP32, for example, was a case of several variations in the millefiori pattern and also in the faceting. Many of this Limited Edition look like completely different designs. It was also a design that had the varied cane letter designating the year of making.