This seems about right. My E12 based E24 has an M90 motor with the car VIN stamped on it. The later E24s were E28 based. Unfortunately I no longer have one of those to check, But we can know that at least up to mid 1980 or maybe as late as 1982, the engines had the VIN. IU'll ask some friends onthe E24 board to check their cars.On older factory cars, this often matched the final digits of the vehicle's VIN, while replacement or newer blocks use standard BMW 8-digit serialization.