I looked at "The Kosta Boda Book of Glass, 1986" which is the Kosta Boda catalogue for that year. It shows Warff and other designs with codes for before 1974 ( for example, 26005, which is a table service designed in 1960), so the code must have been applied retroactively, that is, used on production pieces made in 1974 or later but designed before 1974. Before joining Kosta, the Warffs designed for Pukeberg, which got in financial difficulties in the 1980's. I wonder if Kosta bought the rights to the designs or the rights went from Pukeberg to Kosta with the Warffs. I don't think the engraving is a forgery, which is the perhaps the more obvious alternative. So my guess is that 1961 is the correct year for the design, but not the manufacture.