Product Numbering & Bar Code Verification of Phantom Plarail Sets

A very important set, the C-12 Rotary Snowplough Set (C-12ロータリーじゃせつしゃセット) will be added into the database. The vehicles look like the one in my profile photo. This set makes blind Plarail collectors cry. Fortunately we were very, very lucky to find an owner who is contactable.

Year 1973, G-22, no barcode and JAN number. (Black Tomy Logo, meaning the one with the boy and girl holding hands)

The New International Airport Set, 1978, is G-27. So G-nn could actually represent a year only within the G category.
 

Do we theorise that G-nn numbering system retired in 1978?

We can conclude the G category of numbers belong to the early Hikari-Go mark box art style sets. This means the New International Airport Set and the C-62 Bridge Set are the final sets released in 1978 and the final sets in the early Hikari-Go mark period. (I own the airport set currently) ... The next part of the research is to find the number system of the C-62 Bridge Set. We need to also find what does G literally stand for...