Start with the evidence
Locate the accepted payment terms and the event they refer to. A date based on receipt of a document may differ from a date based on its issue, so keep the underlying wording available.
Work through the example
For this example the parties explicitly agreed 20 October. The review is a direct match between that agreement and the draft, not an assumption about a universal number of days after issue.
Make the next step clear
If two sources conflict, flag the conflict before sending. Record the confirmed date and the evidence used. Avoid creating new late-payment charges or enforcement wording while merely correcting a draft invoice field.
Keep the source context
Treat an invoice draft as a description of an agreed business event. Keep the source agreement nearby and distinguish document preparation from approval, sending and receiving payment. These are separate steps even when they happen close together.