To test whether or not a thread should be discarded do a ( tug test) you pull out about 18” of thread, wrap it around both hands and give a good tug- if it breaks its time to get rid of it- if it’s strong and doesn’t break its a keeper. I’ve had brand new spools of expensive name brand thread that wasn’t usable and I’ve had 40 year old thread still usable. Name doesn’t matter, age doesn’t matter. How it has been stored matters. You can buy thread that was in a warehouse for a long time before it got to the store and heat/ humidity/ packaging wasn’t up to par and it’s no good from the start.