You are correct that there was a run-in, tear-down, inspection, rebuild, and then 2nd run-in. As an engine model matured (fewer faults found) the 2nd run-in was shorted (I believe to 2 hours in the R-2880 B-type.) The power generated in all the run-in's was "captured" in generators and provided a significant amount of electrical power to the engine factory. Large amounts of av-gas were burned.