The six pointed star on the stopper is a feature of another Shape IE bottle I already have so could it be a design feature over the full range of stoppered bottles/decanters/jars or possibly something restricted to those sold by Watsons?
It might be the case that Watsons had a monopoly on "stars in stoppers" as a "special" Monart design. But the six-point star was definitely used by Paul Ysart in his paperweights, and many of those have features which date them to the 1930s period. So it might make sense to believe that the pre-war "stars in stoppers" were a forerunner to Paul's Star Pattern paperweights - or that the paperweights gave an inspiration to the stopper design!!
Perhaps all the stars were initially set in an outline mould but during working many slipped about, and that is certainly the appearance of the one in Keith's bottle, which also seems to show a star outline in mottled blue below the "untidy" parts of the aventurine.
So far, I have not seen or heard of a Star Pattern paperweight that could be attributed to Salvador and that may
be an indication that only Paul worked with stars. But that is an unproven thought on my part and should be treated with a very open mind.
Paul's Star weights also had five points, so maybe that variation could also be found in pre-war stoppers?