Using MIMIC-III (v1.4), it seems that some patients do not have any clinical (i.e. physician, nursing, respiratory, nutrition) text notes during the first 48 hours of their admission. The number ranges from 5-6 thousand depending on whether you use the CHARTTIME or CHARTDATE against the ADMITTIME. There are, however, radiology notes during this period. Additionally, there are about 15k unique HADM_IDs for which there are no such clinical notes at all.
Do these missing notes reflect missing data? An error in the date/time? Or were the patients in the ER, OR, or somewhere else where perhaps the clinical notes weren't captured?