A margin chart that still reads after a price change
When list prices move mid-period, a single stacked bar can hide the story. Here is how we keep the old rate visible beside the new one.
A contribution margin stack that treats the whole month as one rate will smear a mid-month price change into a fake average. The close room then argues about a number nobody actually charged.
We keep two rate bands on the same chart: volume at the prior list, volume at the new list, and a thin annotation for the date the change took effect. The total still ties to the revenue line; the split is what people actually discuss.
If you only have an invoice export, tag each row with the rate in force that day rather than the rate in the current price list. That tag is dull work. It is also the only way the chart stays honest.
Bundlepilotbase can hold those tagged rows as a local record. It does not fetch prices from a venue, and it does not suggest what you should charge next period.