The bolts are likely just a flush fit in the band and not in the ceramic. I seen a couple cases on an Egg where the back of the bolt rusted causing the acorn nut and the rest of the bolt to fall away. An easy, but a minor pain in the butt fix since you have to completely remove the band to get the new bolt into the band.
KJ may be different and have some bolts embedded in the ceramic but I would be surprised if they do. Different rates of expansion/contraction between the metal bands and ceramic might prove problematic.
I also agree that it doesn't appear from the picture Andy references that one couldn't refit the new hinge AND bands on an older KJ unless KJ is also making mods to the ceramics and essentially creating an entirely different new Joe.