When a sales document has been posted we can also view the Promotions that were successfully used on it via the Ribbon, clicking into 'Related' and then choosing 'Promotion Summary'.
The "Promotion Summary" as displayed below shows a list of the promotions that have been used in the document.
This can also be accessed from the "Posted Sales Invoice" ribbon within the 'Related' tab which is useful when wanting to check previously applied promotions.
In addition to this, accessing the "Promotion Code Group" page and clicking into the drill down value for No of Uses will provide a list of documents the code has been applied to.