I recently did an re inspection on a home that had ungrounded three prong receptacles. The electrician installed a GFCI receptacle on the first receptacle in the circuits, and labeled them as GFCI protected, and no equipment ground installed. Awesome.
I was just curious how electricians find out which one is the first receptacle. I have heard electricians call the wiring from circuit breaker to the first device, the home run.
I would find the correct circuit, shut off the CB and then find the receptacle closest to the panel that was off. I would say that the majority of the time that’s the first one. If the cable is visible leaving the panel, like in an unfinished basement, you can trace it to the area where it goes up into the wall. I agree you could waste hours just looking for the first device. In that case a GFCI breaker would work. A MWBC would require a multi-pole GFCI CB.
To find the circuit I would use a circuit tracer first and then go on from there. If you’re speaking of NM cable without ground you’re looking at an old installation. If there hasn’t been much alteration to that old wiring tracing it can be pretty easy.