With all the years I have been doing this
I have hundreds. Some very simple but they really happened. I am sure we have all done this at times when there are multiple units in a building or on a roof top for a building.
I once worked a roof top heater for two days and it was the wrong unit. It was summertime and I was converting it from standing pilot to spark ignition. When I got all done went to the circuit board flipped the switch went to the roof top and it did not have power. Finally discovered I was working on the unit for the store next door. The gas company gave them a free changeover.