Shakespeare’s canon, as it is known today, is incomplete. The Bard is known to have written several plays that were not, for various reasons, included in the First Folio printed shortly after his death.
Other plays, several included in the third folio, were attributed to Shakespeare after that publication, but most are known not to have been written by him, and have since been rejected (called the Shakespeare Apocrypha).
Some, like Pericles, have be given grudging acceptance in the modern canon. Many modern scholars accept Pericles as a collaboration between Shakespeare and a lesser talent (George Wilkins is suggested), but some are willing to accept it as entirely by Shakespeare’s hand.
Other texts have crept into the canon as scholars assess and reassess contemporary works. Two Noble Kinsmen is now accorded a place in most collections as a collaboration between Shakespeare and John Fletcher. Edward III, published anonymously in 1596, has won considerable support as an early Shakespearean history, and appears in many modern collections.
And still others remain contentious. Eric Sams argued well (at least I thought so) for Edmund Ironside as an early Shakespearean history, and his book about the play created a small tempest in academia. Sams’ claim was rejected by some scholars simply because he was not a Shakespeare academic, but rather a talented musicologist.
You can read an analysis of the play and Sams’ claims for authorship here, (a good overview, although the writer incorrectly assumes Shakespeare was really Edward de Vere).
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