Funny, the one I lost before securing the used wheel covers was the rear one on the passenger side. When I looked at the "bite" marks on that painted wheel I could see that some of the wheel covers tabs were not putting heavy pressure/bite on the wheel.

I think that most of the issue is the condition of the wheel cover tabs that "bite" into the wheel to secure the cover. When I installed a set of NOS Mark II wheel covers, they were very hard to put on and they were very hard to remove, tremendous metal screech as I slowly pried them off moving the pry bar around the cover at least 8-10 times to remove a given cover. The fit was a night versus day difference from my used covers which were in excellent cosmetic condition.

To be on the safe side, I added two stainless steel lanyards and extended valve stem retainers as well on each wheel cover. After driving the car quite a bit over very bumpy roads, I checked the two lanyards on each wheel cover and they all were slightly slack indicating that the wheel covers had never loosened.

I removed the wheel covers about 2 years later when shipping the car to Australia and the lanyards were still slightly slack.

Larry