We KNOW that nazeing made glass for S&W- it is an established fact not a hypothese!
It is also true to say that S&W made items specifically for Elwell as shown in the Description Books held at Broadfild House Glass Museum. The colours made by S&W go under the names of: May Green, Mulberry and Puce. The first two are Nazeing names, the third not. Elwell is known to have bought from a number of British companies directly - Gray-Stan, Nazeing, Stevens & Williams, Thomas Webb are certain and were augmented with glass from Czechoslovakia that we know of.
Cyril Manley has often been debuncked since the books' reprinting. Most of it followed on an earlier, American comb-bound publication, which read as if you were looking through Manley's own notebook with his thoughts about who had made each item - but
without proof. The classic mistaking WMF as Ikora was my first insight into this - so you're pushing at an open door where Manley is concerned.
However, where it is noted that items were made for 'Elwell' in the S&W's 1930's Description Books, there is no mention of Nazeing, so I begin to part comapany with you I'm afraid Stephen
These 1930's pieces have very different characteristics to those of Nazeing Glass Works in my experience, which is why we were able to take them out of the Nazeing Room in The Museum of British Domestic Glass and put them in their rightful place - under S&W. The decor/internal decoration does not match that of Nazeing, particularly with the Mulberry, which actually gives a nod to monart with its propencity to have 'larger' granules of colour that form 'pebbles' of colour within the casing. They are heavier, with thicker walls, and the pontils are far more confident that the finishing achieved at Nazeing. The colouring in the Puce items is greatly different from the equivalent pieces known to be Nazeing.
As for the Kempton work being given S&W status, I came up against that problem when trying to borrow from collectors for the Nazeing Glass and It's Origins
exhibition that we held at Lowewood Mueseum back in 2003. The Trumpet vase was aparticular bone of contention, with the number of ribs being quoted as a S&W characteristic by their protagonists, however they are there to see in a Kempton advert that Geoff Timberlake discovered in The Pottery and Glass Trade Gazette.
However, while researching other companies and looking at family collections I have found items that were definately by other manufacturers, such as the supposedly piece of 'Hailware' (by Hailwood & Ackroyd, of Leeds) that was marked 'Pyrex' in the Hailwood family collection. Things can get mixed up and re-attributed within families over a great number of years
Back up information is essentual if you're not going to have someone come out of the woodwork and contradict you after you've published. Yet, there's always the maxim of be the first to publish and those who follow build on your work
Don't know whether that helps? (Or even whether I've made an enemy - I hope not !!)