when was the last time until 07/2105 that patient 84476 was given a platelet count lab test?
select labevents.charttime from labevents where labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'platelet count' ) and labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 84476 ) and strftime('%y-%m',labevents.charttime) <= '2105-07' order by labevents.charttime desc limit 1