This article contains a large amount of information regarding vehicle numbers and identifications, most especially for BMW Airhead motorcycles, but much of this information also applies to other motorcycles, and even your automobile, truck, etc. Information may seem confusing at first. You are advised to slowly read this entire article, and then re-read; and then look at the numbers on your own bike(s), car, truck, etc.
You may be interested in the information in: https://bmwmotorcycletech.info/models.htm and https://bmwmotorcycletech.info/transmission.htm. Those two articles have some further identification information.
There is a LOT of wordy reading here …but, it can be important!
BMW may use different frame and motorcycle identification systems for non-U.S.A. motorcycles. There may be a letter or two letters, followed by a serial number. There may be a serial number followed by one extra number, and then the type of motorcycle. Seven (7) digits are used for the serial number. I do not know what the letters nor the 8th digit means, it could be a check-digit. The VIN system of 17 characters may be absent, in favor of just the Serial Number, with possibly a very small BMW roundel stamping and a letter or two or other number or two. This has especially been seen in later Airheads for ECE shipments. In general, the 17 character VIN system was introduced in approximately 1980-1981.