How will the French authorities check if you have the correct sticker? What’s to stop you getting a sticker for a car with lower emissions (or is that determined automatically on the website)? I also wonder how they enforce this. Are there checkpoints at which gendarmes will check your sticker before letting you through? The other thing is that emissions are often influenced by how well a car is maintained, hence it is possible an older car may actually have lower emissions than the ‘official’ figures. A bit like fuel consumption figures, I suspect standard emissions are based on a lab set up rather than real world driving.