From the observation that Shakespeare got his inspiration from a rather tedious source, follows that the 1597 First Quarto (Q1) took its title from the original bill. Having proved itself a success at the box office, the play eventually returned to the stage as a production of The Most Excellent and Lamentable Tragedy of Romeo and Juliet. Which title adorns the 1599 edition.
As an excellent dating device even for that second production, because it is the header for the opening scene as well : in both editions. Editions that of course refer to the performing company by its current name – obviously – which at the time of the Q1-edition was the Lord Hunsdon’s Men. This was the Burbage troupe from 23 July 1596 unto April 1597, and the fact dates the Q1 edition with remarkable precision. 1 Launched to cash in on the second production, Q1 definitely presents its contents as past history : ‘as it had often been played’. Which suggests a release date shortly after the second production closed. Because it takes time to convert a manuscript text into a pile of printed Quartos, the second production’s closing night must have been about Christmas at the latest, from which follows that the opening night may have co-inceded rather accurately with the reopening of the theatres in the late summer or autumn of 1596 after the plague ban from 22 July.
For the reason why both a pirate Q1-edition and an authorized Q2 may have used the second production’s bill for a header, one can only guess. But what clumsiness may have caused the evidently eavesdropped Q1 to reproduce even a printed text incompletely, and to corrupt Q2’s title in the process as thoroughly as its contents, is beyond all imagination. As for this title itself : Shakespeare would already in 1594 have christened his play The Tragedie of Romeo and Iuliet. And because of the copying of the billboards one can be pretty sure that both Quarto’s stem from the same source : the first piece of evidence that there is no such thing as a pirate Shakespeare edition. 2
The Elizabethan new year’s day was 25 March. This should date Q1 spot on in April 1597. Unfortunately, great precision is not necessarily true precision, because there also seems to have been a new year one week after Christmas.
Its effect on the dating in Henslowe’s diary later in 1597 looked like this : Dec. 1597 > Jan. 1597-8 > Febr. 1597-8 > March 1598. The next year he included March in the transition period 1598-9. Buit even without this inconsistency, it is a dating method that doesn’t make the difference in narrowing down the time window that has the Q1 ready for print : somewhere between 1 January 1597 and the news of Carey’s appointment as Lord Chamberlain.
Come to think of it ; it rather is the second piece of evidence, because ‘some speeches in Q2 are clearly based on Q1’ (J. A. Bryant, Jr. & S. Barnet ; The Signet Classic Shakespeare : Romeo and Juliet. 1964/1986 Textual Note).