Authorized distributor or reseller

WD warranty policy for internal drives requires the product to have been bought from “an authorized distributor or reseller.” This raises two questions:

  1. Where can one find a list of authorized WD distributors and resellers?
  2. If, for example, one has two WD drives, both same model & size, and two receipts, one from an authorized dealer and one not, and neither receipt has the S/N of the drive, how can one tell if a particular drive came from the authorized dealer? (For that matter, how can WD tell?)