As I noted earlier, Richard III probably was written in the early part of the 1590’s after Shakespeare completed the three parts of Henry VI; however, Richard III was not published until 1597.  Shakespeare’s name was not on the title page.  In 1598 it was reprinted this time by William Shake-spear, and again in 1602, 1605, 1612, and 1622.  These quartos were “revised and perfected” but at the same time errors crept into the text.  The 1623 Folio edition purports to be revised against a manuscript.   Most editors today work with the 1598 Quarto and the 1623 Folio to arrive at the best possible text. 

I should also note that editors see in Richard III the influence and perhaps even the hand of Christopher Marlowe who was killed in 1593.  It is known that Shakespeare and Marlowe were good friends, and some scholars speculate that Marlowe may have materially assisted Shakespeare in the writing of this play.