As mentioned in the article, if you’ve passed CFA Level 1, you can say you’ve passed CFA Level 1. Ditto for Level 2, Level 3.
I believe you can state you are a CFA Level 1 candidate as long as you are registered for an exam.
I’m not sure if there is any value in stating you’ve failed e.g. CFA Level 1, since failing CFA Level 1 requires no additional knowledge.
Hope that helps!