Exactly, they are there to make you do this 
and wonder what they were thinking whey they put them their.
The only thing I can think of on why they put holes on the bottom of the rear exhaust pan area was for assembly purposes. They probably had some kind of machine that held the rear pan stationary into place while workers did the final assembly of it onto the vehicle.
I believe they were painted separately and not on the car based on another thread I read many years ago about this on Moparts. I can't be 100% certain though about this.
Certainly this makes sense. Time was of the essence. And the last thing they wanted was workers fiddling, tweaking and adjusting the rear pan into place just as another car is coming into view ready for its pan to be installed.
