What does forescore and seven years ago mean?

A score is 20 years. So, 4 score and 7 years ago would be 87 years ago. 'Fourscore' is four scores, i.e.80. But how about 'forescore'? Not yet in the dictionaries, but only due to a misprint. Shakespeare (whoever he was) in "Winters' Tale" uses the Word 'fourscore' in the phrase "wednesday the fourscore of April". Which must surely be an editor's error for 'forescore', i.e. one less than a score, or 19. Perhaps the Stratford man's true birth date, since 19th April 1564 WAS a Wednesday, and the usual date given (23rd April, which would make him only 3 days old at baptism) is only a guess. (A week was the norm). Unless anyone seriously accepts the 80th April, which would, if carried over, work out to 19th June!