I inherited this set of gold-tone black-enameled cameo jewelry and would like to know how long a patent (as stamped on the back of each piece) would have been used to mark such items. The circular stamp reads PAT JUNE 1811, with a small V in the middle of the circle. The cameo may have fallen out and been reglued to the brooch, because it is upside down in the setting. Would a “modern” manufacturer continue to use this type of mark?

I’m wondering how old and how valuable these might be. Thanks for info you can provide!