good question - not something I'd feel competent to answer really - but as an off the cuff reply I would have thought that with Stuart, the factory were more than likely responsible for naming their own designs. Certainly a lot of Stuart's named decorative patterns go back a long way, and were produced over a longish period.
'Waterford' seems to have been produced from c. 1930s until some time c. 1960s - somewhere I have a couple of large bowls in this pattern.
Of course, the ones to have are the early ones signed by Kny.