True, at least the East German Z80 clone U880 was most likely "properly" reverse-engineered from a real chip's die photos (similar to how the visual6502 netlist

True, at least the East German Z80 clone U880 was most likely "properly" reverse-engineered from a real chip's die photos (similar to how the visual6502 netlist was reverse engineered), with bug fixes applied in the process - because the U880 has a slightly different undocumented behaviour than an original Z80. There are still conflicting stories to this day though (e.g. some licensed clones from other Western manufactures also differed in behaviour in those areas - so the U880 design could have been stolen from those), the only thing that's for sure is that the U880 isn't a "transistor-perfect" clone of an original Z80.