A report is not a portrait painting. I agree that the percentage is rather abstract at what this would entail in reality. And different persons would have different opinions about what constitutes a report done or not done. Surely you could write it in a way, that a mostly finished report would look almost indistinguishable from the finished product.
But it could also be a report where the last % actually concludes the report, like the sum of entries. It would be like an invoice listing all the items, but missing the sum you have to pay. Even if you have all the 99 items there, the crucial thing is the bottom line. And if you leave out some items, the bottom line would be incorrect. And some reports do need to be very correct.