> Who can prove that there was such a notice, long after the packaging is gone? The notice does not matter. Patents cover not only manufacturing and sales, but

> Who can prove that there was such a notice, long after the packaging is gone? The notice does not matter. Patents cover not only manufacturing and sales, but also use of the invention. The patent owner does not need a contract with you, the patent law is enough. If there exists a valid patent, and you don't have permission from the patent owner, then you technically are not allowed to use your widget regardless of what the packaging does or does not say or where you got it from.