Robin Hood is usually set prior to and after the turn of the 13th century,
John having taken the throne from Richard I in 1199. The actual first
mention of him is much later, and in "A Gest of Robyn Hode" (stanza 353) the
King is referred to as Edward, although not by number.
In 1377 he is referred to in "Piers Ploughman".
I have a large collection of material on the subject, brought back from
Nottingham in 1991 and 1994. The most concise as far as dates I historical
references is "On The Trail of Robin Hood" by Richard de Vries, Crossbow
Books, UK 1988,
ISBN 1 869823 02 8.