My pref pane is dated November 6, 2016, and I re-ran the 10.12.4 Combo three days ago, but a flash of inspiration just took me to my "Reinstall To-dos" compilation where I found

Code:
Gatekeeper (Disable/Sierra): sudo spctl --master-disable

I assume that's the answer.

The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire