3rd Party Lenses- Is a good copy a good copy for ever?

This is kind of a follow up post to a recent one about my tamron 24-70. My question here is does anyone know if getting a good copy of a 3rd party lens mean it's going to be good "forever"? Has anyone had a good copy gone bad, either Canon/Nikon or Third Party? via /r/photography http://ift.tt/2uc4AhT