Concise answer
No session number fits every acne-scar pattern. The answer depends on scar type, depth, treatment method, skin response, downtime and the amount of improvement considered worthwhile.
Mixed scars may require different procedures at different visits rather than repeating one device.
Healing intervals are part of treatment because collagen change and pigment response cannot be judged immediately.
When evaluation may help
A scar-mapping consultation can set priorities and review points before a staged plan or approximate session range is discussed.