This isn't the article I read but that "guarantee" doesn't mean you can't get denied boarding right at the time of embarkation.
https://www.usatoday.com/story/travel/cruises/2023/11/30/royal-caribbean-passengers-denied-boarding/71749345007/
We were on a "guaranty" and I honestly kinda freaked out. Our TA appears to have status and got us confirmed. I'll never accept a guaranty again. All of our travel, cruise and other, involves our flying intl long and very long distances. Just my NEVER humble opinion.
PS: I can't find my post about this but I got a lot of grief about it .