What to report as impact factor for a journal that had one the year I submitted my manuscript, but not in the year of publication?
Quick answer: the safest is to give the IF followed by the closest year of estimation: IF 3.5 (2013). The wisest is to understand why the journal does not have an IF for 2014: did it change its name, was it withdrawn from the JCR (journal citation report)?  

Impact factors for one year can be available after a few months.  You can mention other sources like Scimago, that may have other figures (eigenfactor, etc).