 Some of them are recognized by the church because we know about them. But God's holy angels are also holy in the way that those people are holy. And so it's a custom in the Catholic Church to refer to the holy angels, and in particular, St. Michael the Archangel, St. Gabriel the Archangel, St. Raphael. Those are the three saints whose names are revealed to us in the canonical scriptures. So it's a custom.