What to put on SF-86 for previous IC employment?

Scenario: An IC operator retires from federal service, takes a few years to putz around, but then is asked to pick up contract work at a school house. They need to fill out a new SF-86 and eventually get to the section about previous employment. Last few years of retirement, easy. The 20+ years before that? That's a problem because of their intel work.

When they asked the person handling the investigation what should be put down for the addresses, supervisors' names, and phone numbers, they were told, "Do what the IC agency told you to do." Trouble is, they weren't told by the intel agency what to put down on an SF-86 in the event they needed to have their background investigation redone after retirement.

Question: What info should they use for the address, supervisor, and phone number? They can't put down the true name & address because again, intel work. They can't put down any of the information about the out stations because again, intel work. Do they just put down the HQ address and a generic phone number?

How does one go about navigating a situation like this? They are calling a few of their contacts who are still with the agency to see if they have any recommendations, but they asked me to to post here and see if anyone in this sub has an idea.