Reconcile the original, credit and actual payment as relevant, and explain the corrected amount used in the case. Do not keep the larger figure solely because it supports a better projection.
Preserve a clear adjustment trail
Identify the affected work and the analysis that relied on the earlier total. Have any material effect assessed instead of assuming every correction is immaterial or automatically invalidates the project. Adjustments are ordinary in construction and procurement, and a file showing none is more surprising than one showing several.
What matters is the trail. Keep the original invoice, the credit note or revised invoice, the payment record and a short written explanation of what changed and why, and keep them together rather than replacing the earlier document. The failure to avoid is the tidy file: a single clean schedule reflecting current figures with no history behind it, which forces anyone reviewing it to take the totals on trust.
Where a revision is large enough to affect a job analysis or an expenditure claim, say so plainly and ask how the analysis was updated. A correction disclosed by the applicant reads very differently from the same correction discovered by someone else. Retain the correspondence in which the change was first raised, since it dates the discovery.