Peter's been pretty generous with his use of the number 1 -- applying it to each metal of each design. So, there's a number 1 Shimoda in SS, RG, YG, and (not sure, but probably) WG. Then the serial numbering goes up from there within each metal. For some of the Piccadilly's there may even be number 1s for mixed metals (e.g., SS with RG stem and lugs).
The unique pieces are labeled as such, generally with the notation "1/1"
Hope that helps!
Best,
Gary