I'm just learning this fine song. I'm using the Peter Bellamy 1974 recording of "Alan Tyne of Harrow." He also says he got it from Ewan MacColl who got it from an 18th century broadside. So that's at least 59 years earlier than the Bodley broadside mentioned above.

I find nothing to add to the above posts in a web search today.
Has anyone (John? Wolfgang?) come on any additional information on the broadside MacColl refers to (or any other) or the actual historiosity of Alan and/or Valentine?