The dating of Shakespeare's King John depends upon its relationship to the anonymous Troublesome Raigne of King John, a polemical history play which was printed in two parts in 1591. While the plot and sequence of the Troublesome Raigne's scenes are similar to those of King John, the two plays share few linguistic parallels. Those who identify the Troublesome Raigne as Shakespeare's principal source comfortably date King John in the mid 1590s, sometime between the conclusion of the first historical tetralogy and the composition of Richard II. A minority of scholars consider the Troublesome Raigne to be a bad quarto of King John and date Shakespeare's original as early as …
Mason Vaughan, Virginia. "King John". The Literary Encyclopedia. First published 08 March 2001; last revised 30 November -1.
[http://www.litencyc.com/php/sworks.php?rec=true&UID=4236, accessed 28 April 2015.]