It seems like you can't watch a "Christian" TV station without tripping over Apostle John, Dr. Rev. Apostle Smith or someone else called "apostle". I don't recall any of the twelve introducing themselves as "apostle"...
It's a bit unfair to assume that none of the 12 introduced themselves as apostles for two main reasons:
1. Only three of the original 12 wrote books in the NT: Matthew, Peter, and John. Matthew's writing was a Gospel, therefore, he couldn't introduce himself as an apostle since he was writing about Jesus.
2. Peter also introduced himself in his two epistles as an apostle: "Peter, an apostle of Jesus Christ, to the pilgrims of the Dispersion" (1Pet. 1:1) and "Simon Peter, a bondservant and apostle of Jesus Christ, to those who have obtained like precious faith" (2Pet. 1:1).
I've looked in the Bible a few times (lol) and discovered something: remember how Rom. 1 says that God created Creation in such a way that men are without excuse who don't believe that He exists? (In fact, He purposely made among each species, different personalities so that it is basically impossible to believe that since we make things by 'intelligent design', the more intricate things all around us were not made by intelligent design.) Okay, the same way He made the world, He wrote the Bible. But you can't see it (like some people can't see that a God out there created this world) if you do not look for it. "Not everything is written in the Bible, but everything is contained in it." That means that if you say, "Well, the Bible doesn't say I can't do this, so I can", you actually cancel out your reasoning (most people are apparently not aware of that). All this is to say that though only Peter and John of the original 12 apostles wrote books in the NT (six books all together), at least one of them introduces himself as an apostle twice. God allowed this to happen on purpose to cancel out the numerous reasonings that people would have concerning just that.
Peter didn't have to introduce himself as an apostle (
because he was sent to the Jews whom he knew; Paul, on the other hand, was sent to Gentiles who didn't know him and wouldn't automatically receive him as he was a Jew, therefore, it was more sensible that he introduce himself especially with a word that the Greco-Roman world of that day would recognize/understand more readily: apostolos), but if someone, for instance, was to say that because Paul introduced himself that way all the time (except in Hebrews if he in fact was the author, another God thing in my opinion), it means he was not a true apostle, they have to wonder why Peter did it in both of his own writings. What I've found about the Bible is that instead of coming at it with weapons, trying to find something wrong or trying to discredit some teaching (e.g. the gifts of the Spirit being for today), especially Christians should come with tools-- digging tools. The truth is not all on the surface. The Bible covers every little thing and every single topic, but not all on the surface. So, though there are so many false apostles today telling everyone what they dream of being, that doesn't say anything against, for, or with the Bible. The Bible stands alone, and the Holy Spirit its only real (genuine,
certified) Interpreter and Translator.