Just to renovate this topic following some findings of my own.
The Novy Bor link is possible - but according to Ivo's book, "Astera" is the glassworks, not 'Astra', so I'm wondering if there's some cross-pollination of glass going on?
However, my findings take a different slant regarding the Astra label. Firstly, there's a label that's surfaced on a slumped glass item, that's commonly known in the Sunburst pattern:Photo © Gordon More
Here's an example of the Sunburst pattern:
Very Chance-like — but it isn't!
Finally, a press release dated 1966 from Jones & Co. showing the Sunburst design:
A possible reason for these is that Jones & Co were importing glassware made by Spiegelunion Flabeg GmbH and rebadging it using the Astra Glassware label. This might link in with other Astra labels that figure on unrelated items, like blown or stemware.
Incidentally, the designer is noted as being Margrit Thacker.