The last time I checked, T2s and T4s are as follows:
T2 MBI = Subject Interview only; every other lead is Inquiry (I) which means “mailed out” or Linkage (L) which means “computer check.” The only human contact is the Subject Interview between the Investigator and Applicant.
T4 BI = Subject Interview + Personal Interviews of other Sources by the Investigator(s)