Note 14 at 1Co 15:7: There is no individual appearance of the resurrected Jesus to James recorded in the Gospels or in the book of Acts. In fact, it is not certain which James, of the five mentioned in Scripture, this is referring to (see note 3 at Mr 1:19). Most scholars believe this was the James who was the half brother of Jesus (see note 2 at Joh 2:12) and who became the head of the Jerusalem church. This could be a reference to a special appearance of Jesus after His resurrection to His half brother, who didn't believe in Him before the Resurrection (Joh 7:5).

Note 15 at 1Co 15:7: The twelve apostles had already been mentioned, and here, Paul said Jesus appeared to all the apostles. This makes it very clear that there were more than just twelve apostles.

James, the half brother of Jesus, was called an apostle (Ga 1:19). Just two sentences later, Paul called himself an apostle (1Co 15:9). Barnabas was also called an apostle (Ac 14:14).

Some people have believed that for individuals to be apostles, they had to be witnesses of Jesus' earthly ministry, which leads these people to believe there are no apostles today. This is based on Peter's statement in Ac 1:21-22, when they were selecting a replacement for Judas. However, there were hundreds of thousands who saw Jesus during His earthly ministry. Did that make them apostles? Certainly not. There was more to being an apostle than just seeing Jesus during His physical ministry here on earth.

When Paul was defending his apostleship to the Corinthians in 2Co 12:12, he put more emphasis on the miraculous power of the Holy Spirit as evidence of apostleship. In Scripture, apostles are the highest authority in the church, with what many today would call a missionary calling (see note 18 at 1Co 12:28). These individuals still exist today.

Eph 4:11 lists the apostle as one of the ministry gifts given unto the church. In Eph 4:13, Paul made it very clear that this gift of the apostle was given "till we all come in the unity of the faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fulness of Christ." That certainly hasn't happened yet, so we can be assured that God is still gifting people with the calling of an apostle.