I remember reading somewhere about RC & Holmegaard being joined in some
way, and I know they shared a few designers, but that's as much as I do know.
According to great-glass.co.uk:
[Holmegaard] merged with Royal Copenhagen 1985. Amalgamated with Boda Nova-Höganäs Keramik, Orrefors Kosta Boda, & Venini to form Royal Scandinavia.
The decanter looks late-1960's/1970's to me, though.