My shipping notifications will often describe the service used as "Priority Mail 2-3 days", but the label printed from Endicia says Priority Mail 1-Day or Priority Mail 2-Day.
This causes consternation from the customer's end whose order delivery is time sensitive. Can't you query while you are printing the label to find out what the service time really is?
Lastly, when you CANCEL a label, an email still dispatches with the cancelled tracking number. It's confusing to the customer when he gets the second tracking number which is merely a correction.