2.5 Rewriting: sometimes a piece needs more than straight editing. It might call for a good rewrite without distorting the meaning or soul of the story. Ideally, this means strong copy editing with a lighter touch in the rewrite. There will also be occasions when a little padding with clearly-referenced facts and figures might add to the story.
Do talk to the author where you feel the need. Send back the final edited version to her/him if significant changes have been made. Some writers are happy to have their copy improved. Some hate it. So talking to them and playing back the revised version is usually a good thing.