The way the JW’s used to explain it is that Apostles were only the disciples of Jesus that had originally been with Jesus when he was alive. Their explanation is that until they started the JW organization after Jesus death, all other disciples stopped following Jesus when he was arrested.
Thus nobody today can call themselves apostles (typically this is used as an indication against the catholic and orthodox churches that say bishops and popes are the direct successors of the apostels).
I do know this ignores plenty of key scriptures that the Catholic and Orthodox Church uses, but I guess that’s just par for the course.