A 9-year-old male with avoidant/restrictive food intake disorder was referred for psychiatric evaluation eight months ago after his pediatrician documented failure to gain weight for 12 months with a BMI falling from the 35th to the 8th percentile. At initial presentation, he consumed only five foods — plain pasta, white bread, chicken nuggets, apple juice, and potato chips — and refused all other foods due to sensory sensitivity to textures and colors. He gagged reflexively when new foods were placed near his plate. He had no body image concerns, no fear of weight gain, and no caloric restriction motivation. He was started on a multidisciplinary treatment plan including occupational therapy for sensory integration, family-based behavioral feeding intervention, and low-dose mirtazapine 7.5 mg at bedtime for appetite stimulation. At the eight-month follow-up, he now accepts eight foods (adding plain rice, bananas, and vanilla yogurt), his BMI has increased to the 18th percentile, and his parents report reduced gagging around new foods. However, he continues to refuse meals at school, has not gained the weight expected for his age over the past two months, and his food repertoire has not expanded further in the last three months. Which evaluation of treatment response is most accurate?