I love doing this.
I know you like keeping things brief, so I’ll get to the point as well: the meaning of the word ‘apostle’ really fluctuates between the different books of the NT. Some, like the Synoptics, mostly restrict it as a term for the Twelve (Luke makes one exception in Acts 14:14); others, like Paul himself, employ the word in a more broader sense.
But when the apostles Barnabas and Paul heard of it, they tore their garments and rushed out into the crowd… (Acts 14:14)
Paul, a servant of Christ Jesus, called to be an apostle, set apart for the gospel of God… (Romans 1:1)
Now I am speaking to you Gentiles. Inasmuch then as I am an apostle to the Gentiles, I magnify my ministry in order somehow to make my fellow Jews jealous, and thus save some of them. (Romans 11:13-14)
Paul, called by the will of God to be an apostle of Christ Jesus, and our brother Sosthenes… (1 Corinthians 1:1)
Am I not free? Am I not an apostle? Have I not seen Jesus our Lord? Are not you my workmanship in the Lord? (1 Corinthians 9:1)
If to others I am not an apostle, at least I am to you, for you are the seal of my apostleship in the Lord. (1 Corinthians 9:2)
For I am the least of the apostles, unworthy to be called an apostle, because I persecuted the church of God. (1 Corinthians 15:9)
Paul, an apostle of Christ Jesus by the will of God, and Timothy our brother,
To the church of God that is at Corinth, with all the saints who are in the whole of Achaia… (2 Corinthians 1:1)
The signs of a true apostle were performed among you with utmost patience, with signs and wonders and mighty works. (2 Corinthians 12:12)
Paul, an apostle—not from men nor through man, but through Jesus Christ and God the Father, who raised him from the dead… (Galatians 1:1)
Paul, an apostle of Christ Jesus by the will of God,
To the saints who are in Ephesus, and are faithful in Christ Jesus… (Ephesians 1:1)
Paul, an apostle of Christ Jesus by the will of God, and Timothy our brother… (Colossians 1:1)
Paul, an apostle of Christ Jesus by command of God our Savior and of Christ Jesus our hope… (1 Timothy 1:1)
For this I was appointed a preacher and an apostle (I am telling the truth, I am not lying), a teacher of the Gentiles in faith and truth. (1 Timothy 2:7)
Paul, an apostle of Christ Jesus by the will of God according to the promise of the life that is in Christ Jesus… (2 Timothy 1:1)
…for which I [Paul] was appointed a preacher and apostle and teacher… (2 Timothy 1:11)
Paul, a servant of God and an apostle of Jesus Christ, for the sake of the faith of God’s elect and their knowledge of the truth, which accords with godliness… (Titus 1:1)
Therefore, holy brothers, you who share in a heavenly calling, consider Jesus, the apostle and high priest of our confession… (Hebrews 3:1)
Paul calls himself an ‘apostle’ though he was not of the Twelve; Jesus Himself was an apostle according to whoever wrote the epistle of Hebrews. I don’t see why we could grant that Junia was an apostle (‘one who was sent’), which of course does not necessarily mean ‘one of the Twelve Apostles’. Paul himself attests to the existence of what he calls the ‘super-apostles’.