When my first house was under construction in 2001, I created my own key from the builder’s key. When I finally moved in, my key would then disable the builder’s key. Curious how this work, I disassembled my lock and found that there were (iirc) 8 keys which would open all my neighbors houses, even after they had moved in and had disabled the builder’s key. Of course I rekeyed my house to prevent that vulnerability, but in theory it remains on all my neighbors. I also didn’t disclose the vulnerability.