To give them their correct title, the (Rossendale) claim to be unique, and there's no evidence to dispute that claim. It wouldn't be the first time that someone has got the name wrong when reporting on them - often because they haven't taken the trouble to check their facts.

They've researched their history very thoroughly, as you will find if you visit their website.

I quote: "The Dances spread throughout Rossendale and around the turn of the Century there were at least four troupes. One of these was the Tunstead Mill Troupe who celebrated their half century in 1907. It is from this troupe that Britannia is descended."

Perhaps that answers the question?