Name the source-of-truth file and freeze it
Name the file, freeze it, and write it down at the top of the dashboard. One file, one export, one convention. The moment the dashboard pulls from two feeds with different shapes, the totals start disagreeing and nobody can debug them later. A dashboard that reads from one source and one rule survives the next export; a dashboard that reads from 'whatever' does not. The discipline is small — commit to one feed — but it is the discipline that holds the dashboard together once it is handed off.
Write KPIs with formulas in-line
Each KPI gets one explicit formula, written next to its label, in a row that survives a copy-paste into another sheet. No pivot soup, no hidden helper sheets, no nested IFs that only the original author could explain. The formulas should be obvious enough that whoever inherits the file can change them without re-thinking the layout. That is the difference between a dashboard that gets edited and a dashboard that gets re-built from scratch every quarter.
Document so the next person can read it
A short header — what the file is, what the source is, when it was last refreshed, and which conventions to keep — buys the next person two hours. Add a footnote to each KPI that says where the number comes from, and a small changelog when a rule changes. The dashboard should be readable by the next operator without a meeting. If it isn't, it isn't really a dashboard — it is a one-off in dashboard's clothing, and the next quarter will rebuild it from scratch.