Thanks for the additional comments, Alexander.
The Ingold book that I have, The Art of the Paperweight - Saint Louis is the 1995 version, also published by Paperweight Press. Interesting that the later book does not have quite the same info on Nicholas Lutz and others, as was in the 1981 book.
I agree that the Poinsettia in Kulles (plate 105) is generally similar to the blue one being discussed - it has the same basic layout of stem and leaves. But, being pedantic, I think the pink one in Kulles is better shaped, with much more even working of the petals and with a shorter stem and broader leaves. I know these are points of detail, but sometimes that can lead to an interesting conclusion.
You will have to forgive me for disagreeing, but the flower weight in Sybille Jargstorf's book (left-hand column of page 123) is not at all similar to the Poinsettia shown here, or in the Kulles book. I think it's a form of "double Clematis" as it has striped petals with 5 to the front and 10 to the rear and also has two leaves behind the flower head as well as only two leaves on the stem. And the leaves have crimped edges with no sign of surface bubbles.
The same comments apply to the example in the Rossi book - which is actually stated to be a Clematis and has the same structural elements as the one that Jargstorf showed - except that the Rossi one is indeed on a latticino swirl.
Thanks for the pointer to James Mackay's book - I had not looked at that one for some time. Yes, page 89 has a reference to Nicholas Lutz going from NEGC (referred to by its other name of "Cambridge") to Sandwich. The reference is useful in the discussion of whether or not Lutz was at NEGC as the book obviously uses information from no later than 1973. But as with so many other references and books there is no cross-ref to the source of the "fact". However, I suspect much of Mackay's detail was based on the 1969 work The Encyclopedia of Glass Paperweights by Paul Hollister, Jr.
In Hollister's book, which does include source notes, pages 212 and 213, within the chapter on Sandwich, cover the movements of Nicholas Lutz. There is a source reference (correspondence relating to verbal information from the son of Christian Dorflinger's cousin!!) for part of the information about Lutz making weights in the St Louis style at White Mills when working for Dorflinger.
As with Hollister's book, Mackay lists types of weights made by the various companies. In neither work, is there a reference (that I can find) to Poinsettia weights by St Louis. So this suggests that Poinsettias made at Sandwich by, or with influence from, Nicholas Lutz, had the design based on weights from somewhere other than St Louis.