I had to ask for stamps from landrover for the mrs truck, it's only of value on resale but a buyer looks for things like that rather than calling a dealership to confirm IMHO
Stamps though are pretty worthless, you can buy them yourself anyway and go crazy, I know an Indy garage that has main dealer stamps they got made up at vista print, they were bragging about it when the truck was getting mot'd next door and were offering me a service....I declined but it proves a point