I’ve spent a fair amount of time looking into the history of Gregorian Chant, and I have found the same frustration with it’s early history as I did when exploring ancient music: there is little diffinitive documentation to inform me. Because of this, I think I’ll just explore different chant collections and when I find one that really stands out, I’ll research it individually. I’m not sure if this approach will provide any better or more complete information, but at least it will keep me busy and enjoying chant for a good while!