The reason why some say that old threads should not be used is that the newer machines with a higher stitch speed put more wear/stress on the thread and can break the thread, and the thread can give off more lint which is not good for the machine. I use whatever thread I want on my older slower machines, but hesitate to use anything but high quality thread on my newest one. If I do use an older thread and it passes the "break test," I still slow the machine down a lot. You'll know very quickly if a thread is too old when you start getting thread breaks even though you've put a new needle in. You also need to think about how the quilt will be used. Will it get a lot of stress and wear in its use? Or, is it more of a quilt that will be used for display. If people will be sitting on the quilt or kids may drag (God forbid) it on the floor, I'd use a newer thread just to play safe instead of sorry.