Whilst we're confessing, I think the 1720 date for the earliest broadside of FMM is right. The 1685 date comes from a general comment by Chappell in Roxburghe Vol 1. The general concensus (Mudcat earlier thread, online book on printers and Bodleian)is that Sarah was Charles Bates' widow and he was still printing in 1714. Pepys has lots of sheets printed by Charles B and none by Sarah. This and the fact that it isn't in Black Letter would point to the 1720 date.

Basically we have insufficient early evidence on LL. My own opinion that the earliest extant versions look like burlesque to me could point to an even earlier ballad. The fact that even these versions were burlesqued and parodied in the 19th century is only relevant in that several artistes of the 19th century thought it worthy of further burlesque and parody. However it is possible that whoever came up with the earliest version was not burlesquing a particular ballad but the whole genre. We must remember that what we see as charming and wonderful in these ballads was seen by sophisticated literary people as crude and laughable, hence one reason why Percy and later editors felt it necessary to tamper heavily with them.