I'm afraid that's not it either, Bryn.
As far as I know, pedantically speaking the ascent to top C shouldn't be at that point in the verse and shouldn't be a C either, if the whole piece is in 'G minor'. Rockstro took Mendelssohn's transcription of an ornament made at a time when the Sistine Chapel choir were singing the piece a fourth above written pitch. He put it in the wrong place, and in the context of the 'G minor' version. If I felt so moved as to programme the piece in its traditional form I'd be inclined to call it Allegri/Rockstro since it's so far from the original form of the piece.
I believe there was a baroque ensemble in Australia whose director wanted to programme the Albinoni Adagio. Some polite explaining had to be done...