You should have posted this on the Auto-5 forum. However, your gun is, as Goad named it, from the Why? Series. Read about it here: https://www.shotgunworld.com/threads/browning-a5-16-gauge-serial-number-date-guide.297760/page-34
And here on page 1: https://www.shotgunworld.com/threads/browning-a5-16-gauge-serial-number-date-guide.297760/