hello Georgina - welcome from me as well. When you say you've been looking at 'their site', would be very interested to know whose site that is, please.

We have a couple of links on the Board that carry some earlier C20 patterns for Stuart - I'll try and add them tomorrow if possible. Assume you have had a good look all around the base area for signs of a backstamp - usually an acid applied impression of a company name etc. - they can sometimes be very difficult to locate.
I believe that late C19 lamps were more inclined to have enclosed bowl type shades, but designs often continued for a long time.