Off the original subject, but in answer to Joe's query:

"Are there songs that went the other way across the Atlantic, beginning in the U.S. and then migrating to Europe?"

Assuming my info is correct (always problematic where origins of folk music is concerned), there a Quebecois fiddle tune called "Reel de Ti Jean" which crossed the pond to England becoming known as "Little John's Reel". It then crossed back over and settled in the US, familiar to fiddle players under the name "Liberty" or "The Liberty Twostep".

How's that for migration?