Common where a single volatile input dominates cost. The contract names the index, the cadence and the lag, and the price moves mechanically.
The margin exposure is the lag itself: in a rising market the lag is a straight subsidy to the customer. It is knowable and quantifiable per customer per month, and in most businesses it is never quantified, which means it is never traded against anything in a negotiation.
A secondary leak is administrative — adjustments calculated in a spreadsheet and re-keyed into a price list slip past their effective date, extending the lag beyond what was agreed.