FPN and BPN are Face Plate Number/Back Plate Number, and later on, Face Position Number and Back Position Number. At the time your $1 was produced, the actual plate numbers appeared on the notes, indicating that 233 or more face plates were prepared for printing those multicoloured issue $1s. In more recent times, the plate number no longer appears, and in its place, a position number occurs which is related to the position of that particular note in a sheet of notes.