Is it so wet that it has become partly liquid, and if so have parts of the liquid leaked? The essential constituents don't break down just because they are damp. But if it has actually got so wet that it has partially dissolved into a liquid, and the liquid parts have leaked away, then some constituents of it might have been preferably dissolved and the balance of the fertiliser changed. If it is wet but still all there, then you need to shake the bag to redistribute the liquid bit back into the solid part evenly.