I used the following code to explore whether there are any chartevents that happened after ICU stay:

SELECT ce.stay_id, ce.charttime, ce.itemid, ie.intime, ie.outtime, EXTRACT(EPOCH FROM (ce.charttime - ie.outtime))/3600/24 AS days_diff FROM mimiciv_icu.chartevents AS ce LEFT JOIN mimiciv_icu.icustays AS ie ON ce.stay_id = ie.stay_id WHERE ce.charttime > ie.outtime ORDER BY days_diff DESC; 

To my surprise, there are 407966 records of chartevents that happened after ICU stay. Some of them happened many days or even years after ICU outtime. Compare to the 432997491 records of all chartevents, they are not too many though. How did it happen?