That's true if the core is exposed by removing the plastic. The cores I show have never been molded and if new plastic is added at this stage, the chip has to be turned on a lathe to remove the excess brass from the edges. Could be done, but most would not bother.

That said, I would be suspicious of any off-color brass cores as more collectors that I'd like have had other color plastic added because "they look pretty". Definitely true of the marbelized and sparkley plastic brass-cores.

Real counterfeits of the Harrahs brass $100's were made from scratch in China when the chips were live. Both brass cores and plastic are reproduced and they are very well done!