I can't now find the section showing marks/labels, so not sure whether this one is on the GMB or not - however, can always ignore if it is already on the archives. According to Jackson this indicates a 1960's manufacture (not too long before their demise in 1972, apparently. Amazing how some pieces can survive with a label intact for half a century, or thereabouts - obviously never used.
Ref. '20th Century Factory Glass' - Leslie Jackson - 2000.
P.S. Anne (Mod.) - Only just seen your comments about collecting Diamond marks and Rd. Nos. for the GMB reference site?? Do you now have most, or are you still collecting??