"Mod" can stand for a great many things, and for a good many reasons as well, but it's mainly because every time is Modern Times, no matter how many things get modified along the way. "Modern art" goes back a hundred and fifty years, and "modern dance" at least a hundred. To an aging child of the Sixties, however, the word "mod" still largely evokes the Zeitgeist of Beatles-era London, distilled into the hippiest of all hip places happening at that time, Carnaby Street. We found a modest four cases of Modfi* and one of Modifc* in OhioLINK today (plus 98 and 89, respectively, in WorldCat). You will probably find a modicum of these typos in your own catalogs too, so please modify the spelling of any that you do, some of which may have been sitting around since way before "modern" was modern.
(Carnaby Street, London, from Great Marlborough Street, looking south, September 2006, by David Iliff, from Wikimedia Commons.)