The long teardrop-shaped stoppers break easily. It would be fairly easy, I imagine, to get one made.
I don't know what the letters mean, but I wouldn't think it refers to the colours or pattern, given it's one which is a core range at Mdina, produced almost from the start - it's a Michael Harris design, though mostly produced after he left.
Plastic labels came in in the '90s. (p. 133, "Michael Harris: Mdina Glass & Isle of Wight Studio Glass", by Mark hill)