I found him living with the Hi Tech guys in Twinbrook, with starting traits and some unrelated skills. But oddly, he was not the young adult I made, but an adult, as my real guy is. So I forced aging, and he became elder, forced again, he died. I checked back on my real guy and he seemed okay. I saved none of this, as it was an experiment.
I feel like I need to check the town for cloned wife, kid, and simbots too.
Or I could just rename the guy and let him live in peace. That's probably the best thing, huh? If I find no other clones I'll just do that.
edit: I couldn't rename him without switching households and losing wishes, so I just deleted him. Crossing my fingers, with a designated save file in the bag.