Old news, maybe. Still happening or installed, definately
The old style wire strapped XPDRs are still available, also offering EHS options, although I agree a maintenance mode/programmable dongle that flags an error should ensure this doesn't happen with a more modern unit.
I dont think an all zero address can be unflagged if the XPDR is installed together with a TCAS, as the TCAS checks the XPDR, however if the older style XPDR is installed alone, it can be missed.