The first letter of the stamp on leather goods is a code for the year of construction. A quick google search will give you the key to how to read it. The characters after the first make up a code, known only to Hermes, but speculated to reference the code of the artisan who constructed the bag. This entire stamp is different from the now sometimes included serial number. Serial numbers are not put on all bags and it is unclear how H decides which items get serial numbers and which do not. If a bag has a serial number, it is also a toss up as to whether that number will be included on the receipt. Historically, neither the date/artisan stamp nor the serial number were included on the receipt.