You'll likely run into uninformed agents and managers regarding this policy since it rarely happens. Happened to me at LGA. Print a physical copy for this policy and your PNR that shows you have two free checked bags as the agent might or might not take those papers and walk around every counter and ask everyone else's personal opinion regarding this policy. You'll most likely hear "I've never heard of this" unless you're flying out of DFW.

Just pay for the bags and request for a refund after rather than wasting an hour at check in to argue. I wasted an hour and still had to pay for the bags, requested the refund before the flight depart and processed shortly after arrival.