If the regulator is functioning properly, but more current is provided by a replacement rotor/stator - which produces more heat - and if the current demand is higher than the OE design - and if the regulator and rectifier are subjected to more heat from the now higher output rotor/stator field, the regulator can fail... and yes you'll get an indication on the voltmeter - but the reason for the failure may well be due to heat. So, yes, the regulator isn't functioning properly - but it may be because it got fried by something calling for more continuous current and the resulting heat production was more than the OE regulator could stand.

With a sudden current draw event, you probably wouldn't see it on our voltmeters since they use a heated coil for pointer movement and it takes some time for changes to appear on the meter. Also, if the current output spike was within the alternator battery lead's ability to transfer - and if the alternator itself was cool, there would be little - if any - voltage drop. What you would soon see if the voltage regulator blew as a result of a sudden current spike... is a permanent change to a higher voltage reading.

Keep a sharp eye on your fuel and temperature gauges. There is a voltage limiter coil that's built into the gauge set and limits gauges to 7v. If alternator/battery voltage gets too high, the gauge unit is toast. When that happened to mine (alternator regulator problem), the fuel gauge stayed too high too long and then dropped fast to "E" and the temperature gauge read a little higher than normal. If that happens you have to replace the gauge set (after you fix the alternator/battery problem).

It sounds like you need to find a good auto electric shop. The gremlins you describe can drive you nuts.

Frank