a lot of coils are fine down to quite a low voltage, as part of my job I used to test protection relays in power stations, part of that was the voltage to activate and the voltage when the relay drops out again. while some would need 2-3v to pick up, the drop out voltage was usually around 0.5v, as long as they would operate at the required voltages they were passed, out of thousands of relays tested I only ever found a couple that the coils had failed, the rest of these relays, some over 60 years old were still fine.
Grendel