To link a new Apple Authorized Reseller to your Apple Business Manager (ABM) or Apple School Manager (ASM) account, you must add the reseller's Reseller Number (also known as the Apple Customer Number). The Apple Business Manager User Guide states, "To ensure devices purchased from a new Apple Authorized Reseller appear in Apple Business Manager, add the reseller's Reseller Number in the 'Resellers' section of your account settings." Option B (Organization ID) is provided to the reseller, not added in ABM/ASM, while A and C are not required for this purpose.
Reference:
Apple Business Manager User Guide, "Add Resellers" section.
Apple Platform Deployment Guide, "Device Purchasing" section.