That would not stop a clearance. Possible they were told no on an interim…and that scared them off. Getting denied an interim is not a harbinger of denial. It just means someone with adjudication responsibility needs to review and make a determination. Any stray mark would cause that. Incidents from 30 plus years ago, absent a felony, would have little bearing. Run a crim background check and see if there is something you are not aware of. Otherwise if you have not used drugs recreationally and have a 650 minimum credit score…getting cleared secret should be easy.