The Collaborative International Dictionary of English v.0.48:

Misdate \Mis*date"\, v. t. [imp. & p. p. Misdated; p. pr. &
   vb. n. Misdating.]
   1. To put a false or erroneous date on (a document). --Young.
      [1913 Webster]

   2. To assign an incorrect date to; as, the fall of Troy was
      misdated by medieval writers.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

misdating \misdating\ n.
   The assignment of a date to something at a time when it could
   not have existed or occurred.

   Syn: anachronism, mistiming.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

misdating
    n 1: something located at a time when it could not have existed
         or occurred [syn: anachronism, mistiming, misdating]