All of the data on the customs card is per single item. The data on the license plate is for the box.
The Weight per Item Qty on the customs page is pulled from the Item’s Net Weight on the item card. You can find the source of all customs values here:
All data on the Customs page is sent directly to the carrier electronically. You can still print the commercial invoice if you want to, but that will slow down your shipment at customs because they cannot begin processing it until the package arrives at the border with the paperwork instead of pre-processing it electronically.