Corrosion under insulation (CUI) poses a severe threat to many industries operating at elevated temperatures. One of the most used and most cost-effective methods to mitigate and prevent CUI is by the use of organic coatings. In the last decades the importance of CUI-preventive coatings has increased greatly, and standards for testing these coatings have been published and discussed. At the end of 2018 the ISO 19277 standard was published, forming the first internationally accepted standard for testing and qualifying coating systems for CUI protection. Over the last years an extensive amount of testing has been performed to test and qualify coating systems, but also to provide insight and knowledge about the correlations and differences between various CUI test methods. In this paper, we will present a variety of test results to show how complex it is to qualify coatings to prevent CUI occurring. How do we use the library of results we now have? What does it tell us about real life? Do the various standards give the same conclusions based on the results? Some questions will be answered, and some will be left open.