It would appear according to these scriptures that there were more than 12 apostles.
Act 14:14 But when the apostles Barnabas and Paul heard of it, they tore their robes and rushed out into the crowd, crying out
1Co 15:5 and that He appeared to Cephas, then to the twelve.
1Co 15:6 After that He appeared to more than five hundred brethren at one time, most of whom remain until now, but some have fallen asleep;
1Co 15:7 then He appeared to James, then to all the apostles;
1Co 15:8 and last of all, as to one untimely born, He appeared to me also.
Eph 4:11 And He gave some as apostles, and some as prophets, and some as evangelists, and some as pastors and teachers,
Eph 4:12 for the equipping of the saints for the work of service, to the building up of the body of Christ;
Eph 4:13 until we all attain to the unity of the faith, and of the knowledge of the Son of God, to a mature man, to the measure of the stature which belongs to the fullness of Christ.
Some as apostles 'until'
If we are to say that 'apostles' have ceased, then we must also assume the other gifts of prophets, evangelists, and pastors and teachers
I think there could perhaps be a difference in having the 'gift' and having the office of apostle.
Perhaps the '12' (or 13 with Paul) were said to be 'apostles of Christ' or 'of the Lamb'