Shakespeare most likely wrote more plays than you think; some that aren’t included in your Complete Works of William Shakespeare. There isn’t a lot of original writings that have survived from Elizabethan England and dramatic literature is no exception.
Some of Shakespeare’s works were published in Quartos during his lifetime, about 18. Later on in 1623, the First Folio was published with 36 plays in it and was considered the first accurate source for Shakespeare’s text. Since then scholars have found evidence to attribute more plays to Shakespeare.
Your average Complete Works contains 37 plays, the First Folio only 36. The extra one is Pericles which was not yet published. Now we’re up to 37 plays without much argument. Two Noble Kinsmen was originally credited to Shakespeare and John Fletcher when first published in Quarto in 1634. Many accept that is was a joint effort between the two, but it isn’t included in some complete works editions. So far we’re at 38.