When adding a reference to a load, which of the following are valid reference types?

When adding a reference to a load, all the options listed—PRO Number, BOL (Bill of Lading), and PO Number (Purchase Order Number)—are valid reference types. Each of these serves a specific purpose in transportation and logistics management.

The PRO Number is a tracking number used within the shipping industry to identify a shipment and track its movement throughout the logistics process. BOL is a critical document in freight shipping that acts as a receipt for the merchandise and includes important details about the shipment. A PO Number is essential in managing inventory and procurement and serves as a reference for the business transaction between the buyer and seller.

Given that each of these reference types plays a crucial role in ensuring proper documentation, tracking, and communication in the shipping process, selecting all of them as valid reference types is indeed the correct choice.