I personally am skeptical that there are clone chips per se...I find it more plausible that some chips have defects in the upper 64K and therefore are downgraded to be labelled as 64K or *maybe* to save a few cents in testing (if they do test) the upper 64K. I personally had a stm32 that was supposed to be 64K but turned out to be really a full 128K. YMMV. Good luck...
