Sometimes we do have photos where sponsor decals can't be surely identified. A problem mostly modelers have...or people building a replica of a competition car.
Let me start with this one:Jean-Louis Clarr at the Tour de Corse 1982.
Somebody I know is looking for information about the 2 round blue/white decals in the top corners of the starting number field. I'm pretty sure those are either from the event sponsor or from the organizing club.