What code to use after 90972 for follow-up services with same doctor

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I am seeking guidance on which code to use the day(s) after 90792 for a follow-up with the same doctor that did the 90792. We were once instructed to use 90791 for the follow-up and now that I've helped my supervisor to understand that this is not appropriate, I'm having a hard time figuring out exactly which code would be appropriate. I was thinking 9923*. The patients are usually in outpatient/ inpatient care for substance abuse at a facility and we are billing as a doctors group. Any guidance would be greatly appreciated.
It would depend on the pos. If pt is inpatient, you are correct - you would use 9923x. If pt is outpatient, you would use 9921x.