The one with the hole is so that there is something that actually holds the cover down (just a nut) instead of it just popping onto the posts. If mine didn't have the extra hole, I can guarantee you it would have fallen off already due to the crappy job I did putting the posts in.
2012 Ford Focus Sterling Grey Metallic SEL Sedan
Ordered: 8/6/11 VIN: 9/6/11 Build Date: 8/30/11
Delivery: Originally estimated 9/19/11. Delivered 9/22/11. picked up 9/24/11.
Reacquired by Ford under Lemon Law 01/16/13.