One sign is that the surface of the coin can start to bulge outwards as the rot sets in within the core. I would never claim that the BD is cured, just temporarily under control. You have to keep checking your coins on a regular basis, even if they have never shown signs of BD.
If you have a look on the internet you will find images of the various stages.
If you have a look on the internet you will find images of the various stages.



















