Hi M,
Both the suggestions you make are logical. Unfortunately I do not have answer, but rather a couple of suggestions.
Try contacting Norman S-C through his Glass Gallery down in Cornwall, Or contact the London Glassblowing and Peter Layton to see if they either have records, or can shed some light on your query. I've always found them very helpful, but give them a bit of time.
NORMAN STUART CLARKE GLASS
The Glass Gallery, St. Erth, Hayle Tel: 01736 756577
Arts & Crafts Gallery. Workshop. Shop. Visitors welcome to view glass blowing and the gallery. Monday to Friday - 10 to 1 and 2.30 to 5. Saturday 10 to 1. Other times by appointment.
Nigel