Water heater too hot, possibly caused by low water flow
The final piece of the puzzle reveals what was going on.

What I thought was a 2nd or 1st building shutoff was a shutoff outside the building that only shuts off those two specific bathroom sinks' cold water supplies.

Why!?  Who knows!  It's an old building.

But that explains why those two taps were too hot and why none of the other fixtures in the building were affected.

Another factor was that I was using the kitchen sink faucet to test the water temperature, but those are probably not anti scald.