I may be wrong, but music at that time period was taught to others rather than written down. There was no way to keep a record of who originated a piece. Musicians taught other musicians. Musicians traveled their lands playing for whomever would listen (and pay them with food and board). Where ever they went, there would be the local musicians who would pick up whatever songs were being played as well. There would never be a way to know the author of a specific piece. Unless....they were being sponsored by the very very wealthy....or the church.
Back during this era, music was like storytelling. Rarely written down and spread by other musicians. Many entertainers of the time couldn't read music and played entirely by ear and passed songs amongst themselves. By the time the piece if music made it to someone who was able to write it down, the original author was long gone and lost to the ages
Much of medieval music was church music or troubadour music. Churches tended to be unconcerned with fame, but troubadours were intensely concerned; they were their age's rock stars, carrying stories from town to town and sources of gossip and intelligence on rival kingdoms. Some of the songs created by troubadours are sourced, but many of the songs were "cover" songs, done by several troubadours, and they were not the best at recording the songs as sheet music. It was performance art, and often churchmen good the notes down for posterity.