when did patient 30044 for the last time until 07/2100 receive the ptt test?
select labevents.charttime from labevents where labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'ptt' ) and labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 30044 ) and strftime('%y-%m',labevents.charttime) <= '2100-07' order by labevents.charttime desc limit 1