I will solve your mystery
(sorry if you all already did)
The numbers on the gold indicates the purchase date, yes, you all figured out.
The alphabets indicates the initials of the store you purchased.
YT for example stands for Yokohama Takashimaya, thus, the bag was purchased at chanel boutique inside of Takashimaya (Name of a high-end department store in Japan) at Yokohama area.
The numbers on the silver seal indicates the date the bag was taken into the after-care service. (It does not necessarily mean that the bag had problems and were repaired, but simply indicates that Chanel did some after-care service to the bag)