Just an observation, but I find the 390 bosses to be highly glossy. I'm no paint expert, but it is my experience that anything that has a high gloss finish chips easily. Cars are the perfect example. There is a gaming computer company, Falcon, that uses this high gloss car paint finish on their towers. They are notorious for being super sexy, but highly prone to scratching and chipping.
I think this is the case with the bosses. They look super sexy with all that gloss, but paint durability took a hit. This was probably just an oversight on their part.