A cuttlebone will definately not 'go bad'. The only thing to look out for, is if you put a source of calcium, in a tank with fauna that need lower pH levels. Like crushed coral, a cuttlebone has the potential to increase the pH level in an aquarium.
There really is no need to add more, unless the cuttlebone has completely eroded, and your tank's water pH level has dropped below say 7.0. Or you can just go by snail shells (if you have snails). If their shells look look rough and discolored, then they are starting to erode.
I only had about 1/4 of a cuttle bone to any given tank, when it needs it. But my water is a bit on the hard side, at around 7.8 out of the tap.