Doh! Should have checked Andy D's book! The SGS link is intriguing, but I'm a dullard in this area. Not a member of any society etc - yes I know I really really should, the NPS would be a good start.
The overlay cup is very much 'in the style' of John Deacons but very thin indeed. Top facet then six and six side facets.
I know Caithness made some overlay cups in the 1980's braded as Whitefriars traditional - but nothing listed in the Charlton guide.
I think I will have to hope Allan see's this posting!!