thanks Nigel and very interesting
sorry to digress backward but.............. coming back to the issue of cut glass flower frogs/supports, I've just noticed some relevant information in the Miller's/McConnell volume '20th Century Glass'.
Page 63 shows details from a page from a Harrods (London) brochure advertising 'Finest English Cut Crystal' which the book caption indicates was all Stuart production in the 1920's, and the ad includes a flower support described as 'The Magic Flower Holder' - similar in fact to the example I posted some way back in this thread.
Appears to have been offered in seven different sizes, and if you look carefully at the vases on the Harrods page you can just about make out that the majority have been illustrated with a support in situ.
So obviously a not uncommon add-on in the 1920's but perhaps the majority have become lost along the way.