see http://en.wikipedia.org/wiki/Thomas_Custer - both article ad discussion

Date of actions

Until 1948, official references for the date of actions for which Thomas Custer was awarded the Medal of Honor were listed as 2 and 6 April 1865. However, that year a US Army book on Medal of Honor citations listed the dates as 11 May 1863 and 6 April 1865.[1] Consolidated lists of all Medal of Honor citations were published by the US Senate in 1963, 1973 and 1979 with the incorrect first date of 11 May 1863 and in 1963 and 1973 with the correct second date of 6 April 1865. The 1979 edition published the second date as April 1865 and this would seem to be why the online Army Medal of Honor citations at United States Army Center of Military History [2] has two incorrect dates. The Civil War Army recipient that follows Thomas Custer alphabetically is Byron Cutcheon whose date of action was 10 May 1863 which may explain how the first date for Thomas Custer appeared as 10 May 1863.[3]