This is is a futile argument in semantics. All of the definitions of the English word "classic" (except referring to ancient Greek/Roman art and culture) are subjective. "Subjective," meaning "particular to a given person," "existing only in the mind."
That's my English lesson for the day . It's one of those "chicken or egg" debates that will go on forever. How could TCM possibly have an "official" definition of the word? One man's classic may be boring or even offensive to another. I don't care for Science Fiction, but it's a well-accepted movie genre. From time to time TCM offers "class