Product Numbering & Bar Code Verification of Phantom Plarail Sets

I have created the 製造付番 sheet, with the help of Mr. Nayuho:
https://docs.google.com/spreadsheets/d/1...sp=sharing

This sheet stores all manufacturing numbers that are discussed here, in auctions, in personal collections, and from other people who sends me a DM.

We still do not know what the actual meaning of the alphabet in all numbering sequences. Hence, I will announce a research quest here.
In short, your task is to find any CONCRETE information that DIRECTLY leads to the meaning of the alphabets, and you will be rewarded with a position in our research team.