so, I am in a similar dilema...the car was purchased in a state that has a front plate (OH) and the dealer was "kind" enough to put their plastic dealer frame and Certified Pre-owned paper plate on the front.
I removed the dealer plate and frame moments after arriving home, but noticed that the two holes drilled into the front bumpber DO NOT match up with the dimples in the bumper. The US plate mounting holes are not as far apart as the dimples are.
Are the dimples made for the plastic plate bracket that uses mounting holes wider than the US plate mounting holes?
Are the dimples made for Euro or Asia market plates?
___Added pictures on 12 May 17___
Front Plate on the bumper
Gold arrows are the mounting holes for the US plate
The green arrows are the dimples. As you can see, there is quite a difference. At least from front holes are even.
The front mounting screw(s)
Rear Plate mounting
The rear plate mounting options really have me scratching my head. Are the large circle depressions for the RoW mounting bracket? The two other holes, which are directly into the metal, are threaded and use a machine screw (no picture) to mount the US plate. Is this what Mazda thought was a good idea?? The two yellowish rectangles are the left over residue from masking tape that was used to drill the holes...at least that is what I think.
When mounting the rear plate, I used some silicone around the screws to help keep water out of the holes. I guess I could have used thread-locker too just so I know that these screws would not back out.
Is mounting the plate in the rear bumper that hard? It would look much better and the rear hatch could be resculpted for a cleaner look. That's what VW did on my GTI. The plate is in the bumper and the hatch is nice and smooth and blends with the body.