The other number tag is the Body Number plate.
The Body Number plate is plain aluminum upon which is stamped a four-digit number followed by a number of up to five digits. A prefix "JM" or a suffix "L" may also be present, and later cars also have the type designator e.g.: "BJ7", "BJ8", etc. Some late BN7 and BT7 tri-carbs may have the appropriate designator on the body number tag.
The four-digit number designated the Austin purchase order number and the following number designated the Jensen production body number.
The second set of digits on the body number plate, those designating the Jensen production body numbers