Without a proper seal you should be able to see altered frequency response, lower isolation, etc. I'm more skeptical that people are getting the precise insertion depths that someone else may be measuring at, anyhow.
As for canal shape, I'm not sure and also wonder if someone else knows more about that. If I understand correctly, although the shape may be not really "realistic" for a human on most simulators used, the acoustic input impedance and resulting response should be similar to that of some kind of average human ear. It's just like the head / torso simulators use some kind of average human size.
So you don't really get anything but some kind of good idea for those test conditions, not something that can be applied with 100% confidence to any person. In fact, measure the in-ear response using different people and you definitely get different targets.
