We asked an expert who said - "The KG V looks to be right and the date of 1921 would appear to be possibly a stock record on the bottle. This happened quite a lot in the old days as many bottle labels were written on with date, stock number, number in stock etc. It also looks to be a plug cork that may be a bit perished as the level is down into the shoulder. I would hazard itís more of a collectors item than one for drinking."
If you'd like to try and obtain a value, send your photos to mctears.com or bonhams.com. If you do so, please keep us posted on your findings.