I think adaptation is a fair enough word as, whilst essentially similar in concept, the Kastrup ones do vary in shape from the Holmegaard production model, and also in decoration. If anything, the Kastrup ones are much more complex in execution and aesthetics. Also there were probably other designers at other factories producing very similar designs, and possibly pre-dating the Lütken designs. I think there are some basic forms that are used unchecked by more than one glassworks - optic-ribbed tumbler vases, cylinder vases, baluster vases, etc... The beaked vase seems to be one of them (made by Holmegaard, Kastrup and Whitefriars - and probably others).
I've never heard of any instance of Holmegaard outsourcing to Kastrup - they were in direct competition. Although, in principle, it could be possible as Kastrup did comprise of three individual glassworks before the merger.
So sounds like your solution, protem, is to say Kastrup, which we know to be true and "designer unknown" which sounds to me now, like it's unfair to PL.
It's really the only way that I can tackle it without any firm evidence of the design's origins. Plus, personally, I get a little irked when writers of books say that one design copies another because they're approximately
similar when they, the writer, have no evidence that the two designs weren't conceived independently, or that both weren't inspired by earlier forms. It's making a very definite judgement without any facts. Plus design is a very fluid and evolving process and everyone is standing on the shoulders of those who came before. Something should only be called a copy if it's identical, I think. But that's just my own view on it.
PS I thought I read somewhere that JE Bang was Kastrups only designer after a certain date - but I may have got that wrong.
There were other designers at Kastrup during Bang's tenure (1957-65). Bent Severin, Grethe Meyer, Ibi Trier Mørch, Henning Koppel, Tove and Edvard Kindt-Larsen, and Johannes Hammerborg - to name but a few.
Is there any difference in the dates used between the gold and silver labels ?
As far as I can tell they were both used around c.1960 - I've had such a hard time trying to pin down dates to Kastrup labels, as they all seem to have been used in over-lapping time periods without ryhme nor reason. It's a nightmare. c.1960 is probably as good as it gets.
Akvablå = aqua blue ? Would you describe mine as that ? I think I would.
Akvablå as a proper noun is specific to Holmegaard glass, as it's a colourway name, much like Meadow Green or Cinamon is for Whitefriars. But aqua-blue would be a fair description of the colour of your Kastrup vase.