Problem solved.
I asked Iberia.com to send my itinerary via e-mail. The Baggage link (tiny) on the itinerary got me to this page:
https://www.iberia.com/es/luggage/al...aggages-search
After entering my flights' departure and arrival, dates, and purchase dates (but not the booking number), it is confirmed that the checked luggage is free. Rather convoluted :-)