A reporting replacement should begin with a report the team already uses. Rebuilding every spreadsheet at once makes it harder to distinguish necessary logic from accumulated formatting.
Document the current calculation
For each reported field, identify the source and every manual correction applied. Determine whether a correction fixes a source error or expresses a reporting rule that should be documented.
Keep the last completed reporting period as a reference dataset. Explain known mistakes in it instead of requiring the new system to reproduce them blindly.
Build a traceable calculation
Define inclusion rules, period boundaries and treatment of late updates. Preserve enough record identity to explain which items produced an aggregate.
Handle missing inputs explicitly. A blank source should not silently become zero when readers interpret zero as a measured result.
Compare before retiring the manual path
Run the new output against the reference period and investigate differences. Repeat with corrected and late-arriving records. Name the person who approves the reporting definition and the person who maintains the process.
Once those checks pass, decide which manual steps can be retired. See reporting that executives trust for the definitions readers need alongside the report.