Effective June 13, 2011, online retention for Track and Confirm items will be reduced from 60 to 45 days to improve system performance due to expected increases in mailpiece volume, which may slow lookup time. Event details for items more than 45 days old will be stored (archived) in offline files. In these cases, users may make a restoration request online. After a restoration request is made, all event details will be available for future inquiries. Restoration usually takes place within 2–4 hours; however, on rare occasions it may require up to 24 hours.

source: USPS