I’ve never held a security clearance, but my father-in-law did for way over 40 years. My wife and I lived in another state soon after we married, I was told by some of the neighbors that they were questioned about us, they wanted to know why.
This was in the 1970-80’s. I can assure you that it was taken seriously then.
When I got out and worked at Nuke plant in 1986 they called a Japanes friend of mine in Japan. He was shocked