ADNIMERGE provides as much diagnosis information that we have for each participant. Rows with missing diagnosis in ADNIMERGE are often visits where diagnosis is not collected (such as m03). Refer the to the visit schedule to see what was collected when across the phases of ADNI. There may be missing diagnoses at visits from which we should get diagnosis (such as annual visits after m36). The REGISTRY file may contain information about why a visit wasn't done or why only partial information was collected at a specific visit.