For newly recruited participants, RID is in the 2000s for ADNI-GO, 4000s and 5000s in ADNI-2 and 6000s in ADNI-3. There are participants that continue on from earlier stages of ADNI into later stages, so you can either determine they are in a later stage by VISCODE (or VISCODE2) or some files (such as ADNIMERGE) include a variable called COLPROT which defines the protocol for that visit.