Mark,
Only thing I can figure is that it may be to keep the retainer centered on a wheel with 5.7x15 tire versus a 6.4x15.
I also vaguely recall a running change was made to the spare tire well, but I don't know what the scope of that change was - if it affects overall depth.
Not mine, but I attached a photo of a nice survivor car's trunk from the Facebook group. It's not very high resolution, but this car looks to use the center hole.
