Complex sentence: By that time, he had produced, or had been credited with, close to fifty plays--this body of work remained a major part of the King's Men repertory until the closing of the theaters in 1642.
Split into simpler sentences: By that time, he had produced, or had been credited with, close to fifty plays. This body of work remained a major part of the King's Men's repertory until the closing of the theaters in 1642.