I didn't know that at least some of the Customs forms came with limited tracking until I actually asked if there was any way to track international shipments. If there's a barcode on the Customs form you fill out, there should be a number underneath it and that should be able to be plugged into the tracking system. I don't know how detailed the offline info is - I didn't need to use it, as all I needed to know was when the package arrived at its destination.