Hi.....the best thing you can do is research. These would fall into Doulton Series Ware of which there are many. Your right about the dates and series so you have done some research. All of these lines were meant to be collected so all have markings. You can do a lot of it online by looking at different web sites including ebay. Go to your local book store and see if they can order a specific price guide for Doulton plates. The more research you do on your end the better your familarize yourself with precise plates, prices, markings, etc.
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best............... ........Tim
TEACHER: Ellen, give me a sentence starting with "I."
ELLEN: I is...
TEACHER: No, Ellen.... Always say, "I am."
ELLEN: All right... "I am the ninth letter of the alphabet."