Why don't Catholics…use those titles [apostle, prophet]?
Fr. John Hardon defines "apostle" in his Catholic Dictionary as
A messenger and authorized representative of the sender. Broadly used in Scripture, it refers to many followers of Jesus who spread his message. More precisely, however, it applies to the original twelve men chosen by Jesus to be his immediate aides. They are referred to as disciples during the period in which he was instructing the, but following his ascension they are always called Apostles. After Pentecost they spoke and acted with confidence and assurance in teaching others what he had taught them and in assuming leadership roles in the early church. They were ordained priests by Christ at the Last Supper and were commissioned by him to preach the Gospel to all mankind (Matthew 28:19-20). (Etym. Latin apostolus, an apostle; Greek apostolos, one who is sent off.)
Aren't prophets only known to be such after the fact?
For example, Pope Pius XII—in his encyclical promoting Catholic missions, Evangelii Praecones §27—described his predecessor, Pope Pius XI, as having "prophetic vision":
We are profoundly grieved as We behold these conditions which Our immediate Predecessor [Pope Pius XI] described with almost prophetic vision verified in many parts of the Far East.
Pope Paul VI's prediction in his 1968 encyclical Humanæ Vitæ of the damaging effects of contraception to marriage and society has also been called prophetic. He said that contraception "could open wide the way for marital infidelity and a general lowering of moral standards" (§17), which has indeed occurred—e.g., as illustrated below:
(Cf. also Pope Pius XI's encyclical on marriage, Casti Connubii §§53 ff.)