The amount being shown, if you redeemed rewards starting last Friday, is the additional amount you’ll be getting when you reach the next tier, in addition to the weekly rewards you receive. If you are Tier 11, it’s saying you’ll get 75,000 in addition to the 425K you got when you last redeemed, or 500K total.
When you reach Tier 12, you’ll be getting 500K per week (which is the max weekly reward like it used to be for Tier 11 when that was the highest Tier).
This is the same for all Xbox One Forza games.