"If Pepys date of 1666 is correct"
.,,.
How could it not be? He wrote and dated his diary entries on the day they occurred. Why should he have got them wrong?

Samuel Pepys Diary -- January 2, 1666 -- on the fun and games at a New Years party:

    "...but above all, my dear Mrs Knipp with whom I sang; and in perfect pleasure I was to hear her sing, and especially her little Scotch song of Barbary Allen."

Seems clear enough to me.

≈M≈