I'm also a bit surprised that any chorister wouldn't have picked up on the words in The Book of Common Prayer, in which members of the Royal Family are mentioned individually by name. It wouldn't take much to associate the names with faces, especially if the choristers were told they would be receiving an important visit. So, one of the current prayers used every week in cathedrals for example is:
Almighty God, the fountain of all goodness,we humbly beseech thee to bless,Queen Camilla, William Prince of Wales, the Princess of Wales,and all the Royal Family.Endue them with thy Holy Spirit;enrich them with thy heavenly grace;prosper them with all happiness;and bring them to thine everlasting kingdom;through Jesus Christ our Lord.
Amen.
I know all this because DH was, and still is, a chorister!