Hi Chris - unfortunately, I don't know for how long, and between what dates, the Stratford Rings design IN THIS BLUE was produced - as a service, of course, it seems to have lived for almost ever - 1920's apparently into the 1970's.
According to the books, Stuart were still acid badging with their name during the 1960's - and have to say that oddly I've never seen a label - perhaps they all get washed off by the time I see their glass.
I wasn't entirely sure if you were suggesting that between the dates you mentioned, Stuart used a label only, and weren't applying a backstamp.