Answer: You are correct. Liaisons can provide unaccompanied homeless youth verification letters for students who have graduated if you are still in touch and still have knowledge of the information necessary to make the verification. However, you also are right that you should not write letters for former students if you are not in touch with them and aware of their current living situation. In that case, and assuming the youth is not connected to a HUD or RHYA program (as most are not), the financial aid administrator at the university has both the authority and the obligation to make the determination.
Here is a quote from the US Department of Education’s Application and Verification Guide for Financial Aid Administrators (page AVG-117):
“If a student does not have and cannot get documentation from any of the authorities given on page 27, you (the financial aid administrator) must determine if she is an unaccompanied youth who is homeless or is self-supporting and at risk of being homeless. It is important to make homeless youth determinations on a case-by-case basis.”
The AVG goes on to explain the process for FAAs to make the determination. You can access the AVG here.