Fender Tag

Am looking to add another vehicle to my stable and had a question about fender tags and VIN tags.
Both the vin number and fender tags in this car are attached via philip head screws rather then rivets and i've been told that this is not legal and they should be attached with special rivets.
What can you people tell me about that? And should I be concerned? The previous own only had the car for two years and was bought from a dealer.
Thanks