I strongly recommend the Protestant Theological Dictionary of the New Testament edited by Gerhard Kittel and published by Eerdmans. The lengthy article (pages 398-447, Volume I) links "authority" with being "sent" in both NT Greek and usage and in the word Shaliach (which apostolos seems to translate in the LXX.)
And while I'd agree that we all have an apostolate and are called and even "sent" to be "witnesses", I don't see how the Pauline corpus can be understood as saying everyone has the same kind or degree of apostolic authority. Again the I COR12 passage seems to apply.
The article points out that Apollos is never called an apostle, and Timothy is called an adelphos and a synergos tou Theou, but NOT an apostolos.
While the original apostles are witnesses of the Resurrection, not all witnesses are called apostles.
In short, it ain't so clear.
I Cor 12,13,14 go together.. ch 13 is just the comic relief.. Ch 12 and 14 are very serious..