when is the last time patient 9619 had the minimum value of potassium until 42 months ago?
select labevents.charttime from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 9619 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'potassium' ) and datetime(labevents.charttime) <= datetime(current_time,'-42 month') order by labevents.valuenum asc, labevents.charttime desc limit 1