That's been one of the problems. Myco presents in varied ways. The bacteria has a slow growth rate. Therefore, it's often considered a wasting condition where the fish loses overall condition. There is often not anything definitive that someone can point to and have an "Aha, I know what I'm dealing with" moment.
Sometimes, people notice lesions, or bloating, or dropsy, or other signs. Other times, the condition causes stress on the immune system, allowing secondary infections to set in. As a result, the fish dies from Columnaris or another disease.
As for the graphite fins, I suspect that as the organs die, it's the extremities that are affected first. For people, that would be feet and hands. For fish, it would be fins.
One of the issues with using antibiotics and/or other treatments is that they aren't effective against Myco. (It has a waxy coating which protects it.) But using antibiotics will kill the competing bacteria in the tank. This allows the Myco to have better access to nutrients, which actually promotes its growth (although it continues to remain a relatively slow growing type of bacteria).