What causes leaflets reducing? They look happy and healthy

Stress is known to temporarily reduce the number of fingers on a leaf. Genes are expressed, not dictated.

Sounds like the topping has done this. I have never noticed this on my plants but not monitoring it, Id trust Organoman's advice they are a seasoned grower.

This often happen when the plant approaches flowering and is normal. It seems topping can also trigger the plants to remain at the leaf style as when the topping occurs. Neither leaf trait is an area of concern, the plant will continue to grow and flower as its genetics dictate.