Motors will tolerate surprising amounts of excess voltage without damage, if the circumstances are correct.
First, the _insulation_ system in small motors is essentially the same for a 120V single phase motor or a 480V three phase motor; just like the insulation on 'low voltage' building wire is essentially _all_ '600V' insulation. So applying 277V to a 208V motor won't immediately bust through the insulation.
Next, AC motors draw both 'magnetizing' current (reactive volt-amperes) and 'torque producing' current (real volt-amperes). When you increase the voltage to a motor, the magnetizing current goes up; add too much voltage and the iron becomes severely saturated, and the magnetizing current will go way up. But as the magnetizing current goes up, the 'torque producing' current _under load_ goes down. Then means that over some part of the voltage range, the total current actually goes _down_ as you increase the voltage. Raise the voltage still more, and the total current starts going up again.
Finally, what kills the motors themselves is _temperature_, eating away at the insulation or the bearings. When you overload a motor, either with too much magnetizing current or too much load, then it produces excess _heat_. Not excess _temperature_, but heat, which causes the temperature to start going up. If you leave a motor in an excess heating state for long enough, then its temperature will get to high and it will fail. But if you put a motor in an excess heating state (overload) for a short enough period of time, then it will never get too hot, and will remain essentially undamaged by the overload condition.
I presume that these motors were significantly overloaded by the excess voltage. However there were probably only used for short periods of time, and it would take them quite a while to show any sort of damage.
Since these are single phase motors, I would be concerned about any capacitors connected to them. If these are capacitor start or capacitor run motors, then the capacitors may have rather lower voltage ratings than the insulation system.
-Jon
