"Engines in the field" is different to engines in a test cell. The test cell can't tell you whether what is measured results in greater longevity in service or how much.
the most sophisticated piston aero engine test cell on the planet
Who told you that? I haven't done a survey, but this sounds like marketing fluff rather than true facts.
The guy who consults to the auto engine manufacturers and race teams told me that this stuff is well enough understood that test cells are not used as much anymore by manufacturers. Most of it can be modeled by computer. The test cells are mostly used to validate the important data points.