Recent and past drug use, Incriminating other fed employee(s), Moderate-risk PT

I’ve been reading about disclosing recent and past drug use during any PT or clearance process, and I have learned a lot. I appreciate your time and answers.

I have a question about what happens after naming another federal employee during a BI interview.
Suppose “Person A” is getting their interview for PT or clearance. They are forthcoming about recent (within a year) and past drug use experiences, exclusive to marijuana. The investigator would like to know names of people with whom PersonA did drugs with, who they got drugs from, and ideally contact information. Person A names “Person B” as a source and a fellow drug user in the marijuana use, but doesn’t give contact information because they began to dissociate from Person B, stopped contact, removed Person B’s contact info from their devices (and is forthcoming about this dissociation).

Person B may have Public Trust or be in the BI pipeline for the first time, and didn’t disclose their own past MJ use during their e-QIP or interview.

If Person B is already working as a federal employee in a separate department and agency, will the investigators open an investigation on them, and deem them unsuitable based on lying on their own drug use? Will investigator(s) be more concerned and only focused on the activities of Person A, the subject of the investigation, and use the name of Person B only to have a record or reference of the drug use?

Thank you for answering the questions. The idea is that Person A does not want the name of someone else to lead to investigations of another person, who may have Public Trust but didn’t disclose their own drug use. I understand that honesty is the best choice for anyone’s BI. Any additional knowledge is appreciated.