Many years ago, I owned the VW Golf, I think it's the MK2. It has rust and took back to the dealer, they asked all sorts of questions like: how often was it washed?, what was used as the detergent?, what type of sponge was used?, What wax was used? How much hand pressure was applied etc...
Despite their extensive rust warranty I never managed to claim.
Regarding to the current Jazz, I will sand it down and apply a touch up paint. I don't think I will wants to waste my time..