Admittedly, this is not an area of Scottish numismatics that I'm overly familiar with. Unfortunately I don't have a copy of Manville's Tokens of the Industrial Revolution to hand, which is the best catalogue on the series. I do have access to a dedicated numismatic library in Glasgow. I shall check their copy when I'm next able (probably sometime within the next two weeks) to see if the host coin date is listed for this countermark.
A lot of these Scottish countermarks are known from just a few surviving examples, so it wouldn't be unusual for new host coin dates to come to light (and quite exciting).
