Stuart Drysdale told me that all off the glassware they made was by Chic Young and marked with an impressed 'P'. These P can be very vague but clearly identified pieces have been seen without any trace of this 'P'.
In the times that I saw it in their factory shop, every piece on sale was marked.
Stuart also told me that he sold a large batch of their Tulip lamps to a well known Perth antique dealer without fittings - on the understanding that they were for export to Iberia. But they appeared on the market with fittings from the 1950's described as Vasart.
Chic was trained at Moncrieff by Paul Ysart. Do check out the article by Gary at http://www.ysartglass.com/Otherglass/ChicYoung.htm