Sources of the Play
The Third Part of Henry VI, like the Second Part, is based upon an earlier play, which the reviser expands largely and in an independent spirit, but without the introduction of new plot material, and apparently without further study of the historical sources (chiefly Halle or Holinshed). The sole direct source, then, of 3 Henry VI appears to have been this basic play, The True Tragedy of Richard Duke of York, of which printed editions survive from the years 1595, 1600, and 1619. There is reason for inferring that the manuscript version which Shakespeare employed when he produced 3 Henry VI gave a somewhat fuller, and perhaps otherwise more faithful, version of the original play than that found in any of the three printed editions.
The revision by which The True Tragedy was transformed into 3 Henry VI was very thorough, but decidedly less thorough than that which The First Part of the Contention underwent in passing into 2 Henry VI. Whereas the latter play contains about 2150 lines of new or recast matter, 3 Henry VI contains only about 1550; and the reviser's work in 3 Henry VI consists much more in brief casual additions or in alterations which affect the metre rather than the meaning, rather than in such long rhetorical insertions as particularly characterize 2 Henry VI. It would appear that when Shakespeare came to rewrite the later of the two plays, he had somewhat abated the revisionary ardor that led to the elaborate poetic improvisations (often of dubious dramatic worth) with which he so generously interspersed the text of 2 Henry VI.