Richie,
I'm sure we have discussed the date somewhere before. I'm not sure where David got his dating from but Sarah was probably Charles' widow. It is Charles who was printing c1685 so Child was wrong. Charles seems to have had several outlets over the years c1685-1702. The only concrete date I have for Sarah is 1714 so of the 2 I'd say David was the closest and anyway you would expect someone studying currently and in London to be more accurate than someone studying over a century ago in Boston. Child was possibly taking his dates from Chappell/Ebsworth who tend to be rather hit and miss.

Talk/take. I don't follow your reasoning. You can't alter historical documents just on a whim or hunch.

grove/grave
Grave certainly fits the rest of the sentiments in the verse, and may well be a folk-poetry-abbreviated version of 'green grass growing over the grave' very common in traditional balladry.

Arbitrary changes: the apprentice compositors who put together the type weren't too fussy about accuracy. These sort of mistakes are common on broadsides from one pressing to another.

4) 'From tradition'. To which tradition are you referring? If you mean oral tradition perhaps but not necessarily. There is insufficient evidence to draw any conclusions here other than 2 of the stanzas can be found in KotBP. These stanzas may have been written for the play and incorporated into a later ballad, but there are many other possibilities.

I haven't got a record of when the ballad was first registered but I don't have access to the full registers.

5) I have the original correspondence between Chappell and Ebsworth about Mallet's ballad and as soon as I get time I'll check it for you.