Richie
I haven't got time to look now in detail but a short survey of printed ballad lengths might give you a clue.

All printed versions contain your verse 4.
The earliest printed versions ranging from about 1670 to about 1750 have only 19 stanzas. Some time about 1780 it acquired 2 fresh stanzas which could be referred to as commonplaces. These are sts 13 and 19 of the new 21 st version which continued to be printed into the mid 19thc and beyond. This includes American printings such as The Forget-me-not Songster c1848. Unusually there is an 18st version printed in 1776 which lacks not v4 but v5. If a version could be printed which lacked v5 then that begs the question could an American version have been printed about the same time that lacked v4. It seems likely that Deeming or Coverley would have printed such a popular ballad.