You know, after a bit or research with a manufacturer to refer to I think you are spot on. Fits with catalogue pictures of their Liverpool and the use of a metal roundel held by a pin matches too, with mine broken off.I have a late ‘80s GBD that has a 4 digit shape number and the “London Made” stamp. It has the GBD rondel on the stem. Could your dot be a vestige of a rondel? Either way, it is a good looking pipe. I hope it smokes well.