Hi
There are lots of difficulties with much of the recently posted conjecture. Without the evidence before us our hands are largely tied. I still find it difficult to believe that two people claim to have seen a black letter copy, one of them such an antiquarian as Dixon, and no copy has apparently survived. Apart from which someone like Dixon would surely have published it or passed it on to the likes of Furnivall, Chappell or Ebsworth to publish.

Richard Marshall would have been later 18thc and a printing by him would be very plausible.

It is quite difficult to say with any accuracy when black letter finally died out. The normal general date is 1700 but some printers would have gone on after this. 1720 looks like a reasonable guess to me. Some of the later 18thc printers right up to 1800 and beyond used the odd blackletter on the title pages of chapbooks, songsters and garlands, but not for the small print. Whereas a useful number of 1680s 90s broadsides were dated very few ballads were dated after 1700.