I'm always uncertain as to what the exact name for the different sizes was. When I wrote the book I had a single 1976 price list to go from, and even this contained descriptions that had changed over time to meet new purposes (olive tray became ice-cream tray, for example). Also, how far does the sides have to be before a plate turns into a shallow dish? Or how large does a plate have to be, before it is classified as a tray, or even a platter?
So I would tend to think that a plate approaching 10-in. (correct usage, as Christine is probably watching!) is more likely to be a tray.