US Stamps have the same situation. Krause can't use the Minkus & Scott numbering system. There is a printed cross reference and it's probably on the web somewhere.

No opinion, just and observation that coins and US stamps and I'm sure many other collectibles have the same situation. If it's something that isn't numbered by the maker and there isn't some standard of the industry that isn't propritary, created by the authors, then you will find alternate numbering systems.