Well, I didn't know any LATIN chant (plenty of English polyphonic chant) until I got under the tutelage of our current choirmaster. Now I know LOTS of it by heart! The Magnificat (both chant and faux bourdon), Salve Regina, Alma Redemptoris . . . this guy apparently has the whole book committed to memory and wants us to catch up with him ASAP!
It's wrecked my Classical pronunciation though. I sound as Italianate now as any extra in The Passion. < g >