Leads, leads, and more leads, then disclaim.
For every component, ask the subject for leads and don’t stop asking. Case type and issues will determine how many sources are needed, but don’t stop at two or three leads. All too often a source won’t be available, won’t cover the entire time, or won’t talk about issues. Getting as many knowledgeable sources is crucial.
Secondly, communicate those leads. Depending on which contractor you work for or if your fed, you’ll either have to report them in the report or send a case message. I say do both and CYA.
Lastly, disclaim that subject was asked and couldn’t provide any additional leads for A, B, C, and D. As a reviewer, it drives me crazy having to reopen a good report because the investigator failed to obtain and share leads. Seeing that disclaimer closes the door.