How can middleware protocols update operator rewards?

Looking at this file (eigenlayer-contracts/PaymentManager.sol at master 路 Layr-Labs/eigenlayer-contracts 路 GitHub) it looks like the amount of rewards claimed by an operator is not actually calculated on-chain but rather is secured by the off-chain fraud proof challenge period, where the operator can request an arbitrary amount of rewards, but if lying will be slashed in the challenge period and of course will not receive the rewards.

How will this work when protocols are adjusting the reward rates multiple times in one period between the operators last payment until toTaskNumber?