Originally Posted by Prism99

Well, maybe. Cotton thread is subject to dry rot. Also, the process used to dye the darkest colors (such as navy and black) are the most caustic and hardest on the thread. Polyester is not subject to dry rot and I think the color issue is not there for it either.

If the cotton thread was stored in boxes, then it's more likely to be fine. Cardboard boxes allow the thread to "breathe". Storage in plastic is bad for thread because it traps moisture in the thread. Moisture is very damaging to thread and fabric over time.

Where you live can make a difference. If you live in a humid climate, it is more likely that older thread will be damaged. If you live in a dry climate, thread can last a lot longer.

Google "dry rot in thread" for more info. Dry rot is actually a fungi that thrives in damp conditions. It weakens thread and the fibers in fabric.