Not sure about all being marked.
But there is a company ” Decora Ceramics Inc ” in California.
They have peices identicle to Blue Ridge.
Leads me to believe 1. an artist from Blue Ridge worked in California also or 3. Maybe Blue Ridge had pieces made and this other company put their stamp mark on it. Or 3. Some one in California did a great job copying Blue Ridge.
I don’t think Decora marked all their pieces.

Doug