Steve: The following are my thoughts on this:

I would not be looking for shorted turn with this test the growler will pick that up.

I am not sure that this test will pick up fine faults on all rotors that come in for repair.
Each winding on a rotor is supposed to have the same number of turns (controlled at coil winding.)
Sometimes the winding will be too stiff to form or install if the coil is wound from a single conductor, or perhaps the required current capacity is not available and the next larger conductor would make the coil too large to fit in the slot.
When that happens the coil winder will take the correct number of smaller conductors “in hand” and wind them as a single conductor ( 2 in hand or 3 in hand) .
When the coil is fastened to the commutator bar all these coils are in parallel. If one or more were to go open in use this test would detect that as even a "15 in hand" winding that lost 1 wire would show a 6 % change in resistance. 15 in hand is more than I have ever seen but it is possible. It will detect a completely open coil when the rotor is turned to the bars that present the open coil as the main coil.
If the rotor is wound “in hand” and loses 1 section of a coil the following would be expected.
In use the motor the motor would run and probably be fine on a non critical load but it would have a vibration problem caused by the missing coil section.
If the motor were in a closed loop system alone or as part of a larger system it would affect the accuracy of the system.
Certainly it would not live if asked for 100% output but that is not a normal event 75% load is more reasonable.

This application is almost an implementation of a classic 4 wire ohmmeter with application specific output.
Terry