Continuous recalculation is the right answer for most consumption businesses and it introduces three problems that per-deal plans never have.
Usage falls, and so does a commission you already paid. A customer that drops from $120,000 to $70,000 takes the rep's earned commission down with it. This is arithmetically correct and it is the single most disputed thing in consumption comp. Decide up front whether adjustments are capped, whether a floor protects previously paid amounts, and how far back a correction can reach, then write it in the plan rather than settling it per case.
The rep's number changes without anyone touching it. In a seat-based plan a commission only moves when a human edits something. Here it moves because a customer ran more queries. Statements have to show which usage figure produced which payout and when it was last recalculated, or every conversation starts from zero trust.
Month-end stops being a close and becomes a snapshot. There is no moment when consumption is final, so the period close is a decision about which usage reading you are paying on. Pick a cutoff, apply it consistently, and expect the following period to carry adjustments from the previous one.