The only guaranteed sell out is the actual 50th weekend, monorail resorts sold out months ago for that. Still plenty of availability afterwards. Always expect discounts, but the amount may vary depending on how they can fill resorts. Could be limited based on affinity groups (maybe we see another Visa promo, AP, etc). Always book where and what you can afford if there’s no discount and monitor or work with a TA who will do it for you.