Actually, the center caps are not the same from rim to rim. My 13" VX rims are a PITA to find matching center caps for - I have only two of them. I snagged a pair from an eBay sellers, and they are too big for the VX rims, even though they are identical in every other way.

The big thing to look for is the diameter of the tabs on the back of the cap. If they don't fit perfectly, they'll either break and fall off, or fit loosely and fall off after the first good bump.

My solution so far is to move them both to the same side. That way if someone sees the car from the left side, they see caps. From the right side, no caps. This is temporary until I jam on some new rims hopefully later this year.