You haven't provided the particular product nor the actual wording of the guarantee/warranty so it's not possible to judge what was said other than the one word you selected to highlight.
So, here's a typical one from a DAP product -- I'm _quite_ sure the one on the product you bought was/is actually written quite similarly and clearly will only cover the application, not that the material will remain in a usable state in the tube indefinitely.
"Lifetime Durability Guarantee: DAP warrants the performance of this product for sealant purposes during the lifetime of your home. If not satisfied with product performance when used as directed,..."
Note that both the definition of what "lifetime" means and the useage/ application are specified...
As stated before, I really hope you weren't _seriously_ expecting the manufacturer or HD to replace these...