Product codes/item numbers for Plarail Thomas?

What are the "true" item numbers for every item in the Thomas range? Engines are assigned numbers e.g. TS-01, TS-02 etc. but they must have an actual stock number. Sets do not have a two-letter/two-number numbering system. Only thing I can guess is it must be the last six digits in the UPC (barcode), which differs from item to item. All I've got so far is from these items in my collection:
335771 - Thomas at the Suspension Bridge Set
826095 - Gator and Marion
968153 - Hurricane and Frankie
977735 - Thomas the Tank Engine Island of Sodor Challenge

EDIT: It seems 1999.co.jp has these 6-digit product numbers for Thomas items going back for at least the last few years.