I think the issue with old thread is that it can become dry and brittle and might jam up in your machine, not that it's too old to hold the fabric together. Seems like I read somewhere once about putting old thread in the freezer to "rehydrate" it. Never tried it. I've got some seriously old thread (large spool priced at 15 cents!) that was given to me by my DH's grandmother before she passed away. So far none of it has given me any problems.