Also does this all knowing company even have an engine development test cell?
According to the quote on the APS website they do:
"
Lycoming is in complete agreement that it is possible to operate an engine on the lean side of peak TIT. It is done on engines in our well-instrumented Experimental Test laboratory every day. There is nothing detrimental in operating an engine in this manner."
Would you really expect that Lycoming would operate without a test cell?
I'm not saying that they are all-knowing. I'm just saying that it's possible that they know more about the engines they build than APS give them credit for.
I also doubt that they just ship engines out the door and never collect in flight data. I would expect that they work closely with airframe manufacturers, including analysis of in flight data for new or changed installations.
What would be the liability for Lycoming if they didn't? Or for Cessna if they didn't consult with the manufacturer? How would it look in the witness box after an engine failure accident?