Many different variables affect how long thread lasts, including the quality of the thread, the thread’s exposure to the elements, the spool’s material, and the thread’s material. You may not be able to determine whether a spool is still good based on how old it is alone, but there are other ways to test whether the thread can still be used.

From this page
https://www.allfreesewing.com/Sewing...Thread-Get-Old