I thought I’d provide a follow up/data point for the future. We arrived to the Iberia Dali lounge and I gave them my business class ticket. The woman scanned it and I went on, no questions asked.
However, when my husband (right behind me) did the same thing, they told him he couldn’t enter. He brought up that they just let me in without issue and I mentioned I read that we could use this upon arrival. After a minute she let him through.