CPT® codes 90801 & 90802

My behavioral health providers (MD's & Phd"s)believe that these CPT® codes can be used twice to evaluate a patient. They argue that the initial evaluation is not completed in a single session. I have thought that these codes could only be used once and the next patient visit was a subsequent visit. Who is correct?

re: CPT® codes 90801 & 90802

A 90801 can only be used once every 6 months per provider number and subsequent visits are billed using a follow up visit code.