I've been hunting through newspaper archives to try and find out more about Millard Norman, and the following facts have been extracted from several newspaper articles about Denby from 1970.
13 March 1970 (Birmingham Daily Post)
The American importer of Denbyware for almost 20 years (i.e. since around 1950) was Millard-Norman (Milnor). In 1961 Lionel Simons, a London-born graduate of the Columbia Business School (USA), became the vice-president of Milnor, later he was its president and sole shareholder, and on its merger with Denbyware Ltd he became a millionnaire and a million-plus shareholder (25%) of the Denbyware group. Milnor's turnover between 1963-1968 was mainly from Denby products.
13 March 1970 (Ripley and Heanor News) In addition to the facts as above, this article concluded with this information: 'The Millard-Norman Company ... trades under the name "Milnor". It does not manufacture goods.'
14 March 1970 (Derby Daily Telegraph) An extra snippet from this article: 'Millard-Norman (Milnor) were ... the sole US distributor of Denby and Langley.'
So, to conclude, we now know that Millard Norman (Milnor) was an importer not a manufacturer and was the sole US importer of Denbyware.
That Denbyware contracted with an (as yet) unknown glassworks in Sweden to provide Denby glassware is clear from the advert I posted above and from the labelled examples of Milnor glass we have seen.
The next step is to identify which glassworks that was, and that might prove a little more difficult to establish, but I'll keep searching.