Jim,
You're making a distinction that is not offered in Scripture, but is rather made by translators. The word "Apostolos," and its many forms (including Apostoloi and Apostellw) all mean the same thing. To distinguish one form of Apostle from another is not an uncommon thing to do, but the language itself doesn't support it. I don't mind distinguishing "The Twelve," whether you include Paul or not, and referring to them as "The Twelve Apostles," but the Twelve are not the only ones in Scripture who are called apostles, and unless we're choosing to use a definition of apostle foreign to the text, we need to recognize that an apostle is one who is sent, and an apostle of Christ is one who is sent by Christ. Luke acknowledges Barnabas as an apostle in
Acts 11, so I consider him to be one. Paul also acknowledges James as an apostle, along with the rest of the Lord's brothers. In
1 Thess 2, Paul says "As apostles of Christ
we could have been a burden to you," with the "we" referring to himelf, Silas, and Timothy. One could also make an argument for Sosthenes, but that's less clear. So in all, at least 5 people (The lord's brothers are at least 2, Silas, Timothy, and Barnabas) are identified as apostles outside of the 12. Given Jesus' statement to Peter/the Twelve about binding and loosing and all authority under heaven, I'm inclined to accept Matthias as an apostle as well, but again, that one's a little fuzzy. Regardless, I am pretty sure that the only way to say there were Twelve and only Twelve Apostles is to play games with the text and the language that I'm not comfortable playing- essentially, you define apostles to include that there were only twelve so that you can say there were no more than twelve apostles. Although your conclusion is in step with your definition, I don't believe it's in step with the Scriptures, either in Greek or in English.