My best estimate is that Report 13 was the initial draft of Battelle's study dated March 17, 1954.  Vallee was the first to find that date in the BB files and noted it in one of his early books but I don't think he saw the actual document (which is not in the BB files we have today).  I have seen a document or two in the BB files that cites the March 17, 1954, date but I don't recall where, and that is probably where Vallee got it from.  I am the one suggesting that this first draft Battelle report was Rpt 13.  The timing more or less fits.  Report 12 was Sept 30, 1953, status reports were becoming more sporadic with the end of the Korean War and the consequent return to civilian life of a lot of military personnel such as Ruppelt and Olsson in BB, etc.