Pasko, Swan and Chiaramonte address the fact that no one realizes Clark Kent and Superman are the same person in issue 330 (Dec. 78), with an explanation what worked for me at age 13.
Spellbinder, a Batman villain from 1966, makes his second appearance in this tale, with a costume that is not quite as garish as the original, but darn close. Spellbinder has hypnotic abilities, affecting people’s perceptions, and even Superman is subject to his powers.
Since he knows that Spellbinder relies on hypnosis, Superman resorts to it as well, hypnotizing people to be immune to hypnosis.
An odd sequence follows this. The real Martin Korda is finally released from the hospital, starting work at WGBS after being kidnapped and impersonated by Metallo. Lana Lang is showing him around, and they walk in on Superman as he is changing to Clark Kent. But instead of reacting as if they caught him, both are puzzled as to why Clark has a Superman costume on. The hero is glad that his secret is safe, but also confused.
He overcomes Spellbinder after figuring out that the villain is using sonics to affect him. Spellbinder comes back, three years down the road, in the pages of Batman.
But the kicker to the story comes at the end, as Clark realizes that he has been using the Kryptonian lenses in his glasses to unwittingly hypnotize all those around him into seeing Clark Kent as a different person than Superman.
It may not be the best possible explanation, but at least it tries.