Flight Modeling vs. Flight Handling.

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While I'm no engineer, I did work on the engine production line of Toyota for 4 years, the last 2 were on the engine testing bays.

No two engines were ever identical. In particular the power output and emissions they produced where all different. While they were within tolerances and differences were very marginal, there were differences non the less. Multiply this by adding other components to the cars (gearbox, drive train etc.) no two cars rolling off the production line were ever the same. You probably wouldn't notice the difference immediately but as the car was used over time, tolerances become wider as the car loosens up and quirks begin to appear.

Saying that two identical cars / aircraft would perform / feel the same is correct, but only on the drawing board. In real life it's very hard to get two mechanical devices to perform "exactly" the same. There will always be some variation in real world products, otherwise we wouldn't need to have warranties would we