This is misunderstood in both directions, and both are expensive. Some practices bill chronic care management straight through a transitional care period, which CMS does not permit. Others disenroll a patient from chronic care management the moment they are admitted, which forfeits the months where the exception genuinely applies. Enrollment is not the question; billing for an overlapping period is.
Because the TCM period starts on the discharge date and runs 29 further days, the calendar decides the answer before anything clinical does. A patient discharged early in the month has a period that ends in the next month, so no CCM claim is possible for the discharge month. A patient discharged late in the previous month may leave a usable window. CMS states it expects that most of the time the two will not be billed in the same month.
The accounting requirement holds regardless. Time counted toward chronic care management cannot be counted toward any other billed code, so a monthly total per patient cannot demonstrate either the separation or that the CCM minutes fell after the TCM period closed.
Separate limits do still apply. Only one practitioner may report transitional care management for a given discharge, and only once in the 30-day period. The required face-to-face visit cannot be reported on the same day as discharge day management. And transitional care management cannot be billed if any part of the 30-day period falls inside a post-operative global surgery period for a procedure billed by the same practitioner.