NVIDIA sells certification exams at a fixed published fee — $125 for associate exams, up to $500 for the most expensive professional one — through its own registration flow. It does not run consumer-style couponing on them: there is no seasonal sale, no first-purchase code, no referral discount. Discounting happens as voucher allocation to organisations and events instead, which is why the routes above all run through somebody who already has a relationship with NVIDIA.
That means every page offering you an “NVIDIA certification promo code” is in one of three positions: it is describing an expired event promotion, it is generating codes that do not work to capture the search, or it is affiliate bait for something that is not an NVIDIA exam. If you find a code that appears to work, check what it is being applied to — it is usually a third-party course, not the exam.
The one genuinely actionable piece of timing advice: exams are non-refundable inside 24 hours of your session but rescheduling outside that window is free, so booking early does not lock you out of a promotion you discover later.