Just so you know, the confirmation name is sometimes used.
My great grandfather was not born with a middle name but was married and later died with the middle name 'Patrick'.
His son, my grandfather, was not born with a middle name and never used his confirmation name.
His son, my father, was not born with a middle name but uses the middle name of James which he was confirmed with. He was married with this middle name and it appears on my birth certificate.
There seems to be no inital clarity on the situation as to why some people use it and other's don't.