UPS tracking numbers are valid for a period of 90 days.
After 90 days the UPS tracking number becomes Invalid and is usually no longer on the UPS website.
If you haven't received the shipment within a few weeks then you should contact the shipper and the UPS to find out what you can do about it.
Sometimes the UPS can track the location of the package if it was dropped off at another address through GPS so you should first contact the UPS before contacting the shipper and give them the UPS tracking number.