Campden Tablet - Shelf Life

I googled this one but didn't find any satisfactory answers. I 'inherited' some winemaking stuff my father used. I've
thrown most of the chemicals out as they didn't smell right, but the campden tablets all smelled as they should. These
are 7 -20 years old though.

I know, I know, campden tablets are cheap so I probably should chuck them too and not try to save money on these things,
but they were in sealed containers and as I say, they smell like my new ones do. I only use campden tablets on initial
must anyway.

So does anyone know if campden tablets keep thaaat well?