As a sewing educator, I see students bring in, ummm, some interesting examples of thread. It is always interesting to me that people will spend XX dollars on beautiful fabric, but don’t consider thread as an important part of the construction equation.
Thread has a life span. It wears out. If your thread label reads 35¢ you can safely throw it away. If it breaks easily when you grab it between yours hands and give a quick snap, into the trash it goes. If it is exposed to dust and light it will degrade faster.
Do yourself a favor and “splurge” on fresh thread. 🙂