FYI, I was using an older thread to attach the binding to the back of a quilt yesterday. After about 24 inches of stitching I tied off my stitching and changed to a newer thread. I then tossed the old spool in the trash. The thread kept breaking, untwisting and shedding little bits of colored fluff. Poor quality of thread? (no label) Old thread? Indeed, but no idea of the age because it was donated to me.
In the end, test the thread BEFORE using it to save yourself the grief of having to re work your stitching.