I don't know about technicalities of historical geographical dividing lines.

I do know that Essex is represented in East Anglian Traditional Music Trust, by Essex County Council, Head of Heritage and Arts.

University of East Anglia is in Essex.

East Anglian Railway Museum is in Colchester Essex.

I will try to remember to ask our Sound and Video Archivist if there is any such Wassail.

Has any thought to ask the Morris Ring?

Also seems to me there could be one attached to Molly tradition which is Essex