###HUMAN: count the number of patients who were diagnosed with valvular stenosis - aortic but did not come back to hospital within 2 months until 1 year ago., ###ASSISTANT: SELECT (SELECT COUNT(DISTINCT t1.uniquepid) FROM (SELECT patient.uniquepid, diagnosis.diagnosistime FROM diagnosis JOIN patient ON diagnosis.patientunitstayid = patient.patientunitstayid WHERE diagnosis.diagnosisname = 'valvular stenosis - aortic' AND DATETIME(diagnosis.diagnosistime) <= DATETIME(CURRENT_TIME(), '-1 year')) AS t1) - (SELECT COUNT(DISTINCT t2.uniquepid) FROM (SELECT patient.uniquepid, diagnosis.diagnosistime FROM diagnosis JOIN patient ON diagnosis.patientunitstayid = patient.patientunitstayid WHERE diagnosis.diagnosisname = 'valvular stenosis - aortic' AND DATETIME(diagnosis.diagnosistime) <= DATETIME(CURRENT_TIME(), '-1 year')) AS t2 JOIN patient ON t2.uniquepid = patient.uniquepid WHERE t2.diagnosistime < patient.hospitaladmittime AND DATETIME(patient.hospitaladmittime) <= DATETIME(CURRENT_TIME(), '-1 year') AND DATETIME(patient.hospitaladmittime) BETWEEN DATETIME(t2.diagnosistime) AND DATETIME(t2.diagnosistime, '+2 month'))