Mettler is great thread! I use it frequently-right color. I have lots of older thread and use it all the time. Part of the question about thread deterioration can be environmental such as temperature, ultraviolet exposure and humidity. I live in a rather cool, dry climate and store my thread in a cabinet so I never worry about this. I have thread that is years old. The break test that you mentioned has several components-fiber content, number of plies, size of plies and amount of twist. If it breaks easily and multiple times in your machine then you should not use it. If it sews in nicely, then use it.