when did patient 21074 get a lab test until 27 months ago for the last time?
select labevents.charttime from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 21074 ) and datetime(labevents.charttime) <= datetime(current_time,'-27 month') order by labevents.charttime desc limit 1