Use this as an object lesson in research! This is the sort of thing academic researchers run into all the time. Was Lassus born in 1532 or 1534? Could this piece have been composed by 1555, when the first performance of it that we know about was in 1560? Or, more recently: what we know as “facts” about Mozart, for instance, is a mix of actual facts, propaganda put out by his father (who surely profited by having a musical prodigy as a son), propaganda put out by Mozart himself, since he knew the publicity value of cultivating a mysterious public image, and hagiography by Mozart’s biographers in the 19th century.
See if your student can read through the different versions and come up with a summary that’s likely to be accurate while acknowledging the differences. This is likely to be better research than finding the one that’s “true.”