Yup, need to keep up the anti corrosion card in the back of the manual.
Also some require that its serviced with them on time for everything up to the point you claim (even though they often don’t do the corrosion card even when they are supposed to, I assume deliberatly).
We had a massive problem with corrosion with an old merc E class, 2000 W reg, bought it 2years old from merc dealer, at its first MOT (not done with merc and their stupid prices) it failed as was deamed unsafe to even bother fixing, entire area where the rear subframe/ suspension cage/ axle pivots etc attached into the body of the car was rotton in so many places that it was technically a write off.
Took over a year of battling with Merc to eventually get the money back for the car (not the whole amount, only difference between £0 and value of car at that point, so catered for merc dealer price deprecations).
Essentially car warranties = hassle you don’t need in your life. Generally even if its even a common fault you have to PROOVE to the dealer/retailer that it is a common problem then argue they have to fix to xxxx standard etc.
I just get tired of it and as a rule of thumb, generally don’t bother buying new stuff of value anymore as you often don’t get as much protection as you think you will.