Just to add to this.
Decora began as Yylyne Studio in Los Angeles in 1946 and Palm Garden Pottery in Inglewood in 1947.
Father and son respectively.
They combined in 1949 as Decora and closed its’ operations in 1953.
If there is any connection maybe this will help in research.

Read the following website, lots of useful information. Answers your question.

[url]http://blueridge-spi.com/pottery/[/url]

Doug

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