How can we track back to our suppliers' invoices or lot numbers with ItemPath?

Supplier Lot Numbers and Invoices can be Items that you can create from.
Set up an Item Type for both Supplier Invoice and Supplier Lot Number.
When you register the Supplier Invoice, you can use Create From Supplier to tie it to the supplier.
Upon receiving the goods, you can first use Create From Item to have the Supplier Lot be from the Supplier Invoice.
Then the goods themselves can be registered using Create From Item to have them come from the Lot Number.
You can receive containers or pallets from the Supplier Lot and later have the cases or goods coming from the containers or pallets.