The USPS will re-use tracking customs numbers after a certain amount of time has passed. Occasionally, customers may receive a customs number that still shows the previous delivery confirmation from the last package it was used for. (For example, a package being sent to France may display information that it was delivered in Canada a year ago.)
This is only because the USPS has not updated the customs number with the correct information yet. Please allow 48-72 hours from the time you receive your shipment notification email for your tracking or customs information to begin updating with the current delivery information!