Keith is correct - complex coding for this factory it seems. The initial letter B is used to signify a vase and the No. 984 (at least that's what it looks like to me) will indicate the year when it was produced. Unfortunately, my book only goes up to code 974 for 1962, so this one may well be anywhere in the following ten years. The remainder of the code will be for the engraved design. The factory suffered a serious fire in 1973, apparently, and was sold to Orrefors in 1976, and closed finally in 1979.
Perhaps if Bill Geary is watching he may know the date for code 984.