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]

WordNet (r) 3.0 (2006):

misdate
    v 1: assign the wrong date to

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "misdate":
   anachronism, antedate, antedating, anticipation, earliness,
   foredate, historical error, lag, lateness, metachronism, misdating,
   mistime, mistiming, parachronism, postdate, postdating,
   prochronism, prolepsis, tardiness, unpunctuality