If you log in to NowLearning, you will be notified about the need to take a Delta exam. If you fail all attempts (or don't take them), your certification looses its 'current' status and it is no longer valid.

A Delta exam needs to be taken once a year and the last one opened in January and closed in April (if I'm not mistaking). So if you didn't take the exam, your certifications won't show 'current' anymore.