I bought a huge bottle of Potassium Bromide in the '50s. It is still good.
The nature of the halide salts is to clump! They all do. Table salt clumps. They put an additive in it to prevent clumping and that is why table salt should not be used when you need Sodium Chloride in a photographic formula.
Sorry to go off thread a little here, but how does the non-clumping additive effect Sodium Chloride in a photographic formula? The reason I ask, is that I have never noticed a problem with this.