I don't think his tail would matter too much actually... but be careful with those holes! It could be a good idea to treat him with some Melafix or Pimafix, they're not really medicines, but they're natural remedies that will help the fish heal on its own But then again, for three months?? Could you post a picture of this fish? I have no idea of what this "black thingy" on his tail would be xD Is it like a lump?

I wonder why the breeder kept this fish at all actually, mainly because of the eye... It's not aesthetically pleasing, and there could be the risk that it'd develop into a problem later on. But for now, I don't think he's very bothered by it, unless it's making him act weird, like swim in strange angles or struggle to do so. It might become a problem when he'll grow old, but he's probably used to it by now