Complex sentence: Its existence as a potential target of the "New Horizons" probe was revealed by NASA in October 2014 and designated PT1, but the official name was not assigned by the Minor Planet Center (MPC) until March 2015 after better orbit information was available.
Split into simpler sentences: Its existence as a potential target of the "New Horizons" probe was revealed by NASA in October 2014 and was designated PT1 ("Potential Target 1"). The official name was assigned by the Minor Planet Center (MPC) in March 2015 after sufficient orbital information was available.