One record from the enquiry to the final invoice.
Every job starts as an enquiry (E-) and becomes the quote that wins it (Q-), the job itself (J-), its invoices (INV-) and its purchase orders (PO-) - on one card, with its revisions, its variations, its documents, and who did what, when. Nothing is retyped between them, so the invoice can only say what the accepted quote said.
A revision is a new document, Rev 2 beside Rev 1. The one your client already saw stays on record exactly as they saw it - a sent quote is never rewritten.