Mera spored mera

I saw this film on video tape in the home of a friend of a friend in Sofia, Bulgaria in 1982 or 1983. I don't remember much about it - one rather heavy-handed anti-Christian scene where a character believes he has seen a saint or an angel, but where the viewer is shown in a very pedagogical manner that it is an accident (or a practical joke?) and a trick of the light. The other thing I remember is the reason why I wanted to see the film in the first place. The film is (purports to be) historical and is set in the early years of the 20th century pre-WW1. The protagonist is involved with a group of nationalist freedom fighters, operating in Turkish controlled Macedonia. They kidnap a Protestant Christian missionary, Miss Stone. ("Mis Stoun" in this cast list.) At some point, to calm the savage revolutionary beasts perhaps, Miss Stone sings them a Christmas carol, "In the Bleak Mid-winter". The interest for me was that Miss Stone was played by Christine Bartlet, ("Christin" in this cast list), who was my colleague at the 114th English Medium School. If I remember right, though Miss Stone is supposed to be an American, Christine's Glaswegian accent is very apparent. I think the song was an ad lib - and therefore just possibly a goof: "In the Bleak Mid-winter" is originally a poem by Christina Rosetti and was only set to music (by Gustav Holst) in 1906. So for the song to be appropriate, the action of the scene must fall between 1906 and 1912 (the first Balkan War). But was the song so very well known, even then, that an American missionary would think to sing it under those circumstances?