As well as indicating the card status in terms of written, mailed etc. you can also (version 7.1 onwards) indicate that the item is “completed”. Use this as you like, but you could use it to indicate that the card/mail has been hand-delivered, or the eCard sent etc.
To mark items as Completed, you must be in Edit mode – tap the Edit button on the top-right, to reveal the checkboxes on the left of each name. Select the items that are completed. Then tap the Change Status button (square with tick inside) on the bottom-right.
From the popup menu, tap on Mark as Completed. (Note: if you change your mind about an entry or entries, you can repeat this but tap on Clear Completion Status”.)
Entries are then shown as being Completed by showing a tick after the name.