Everything The Beatles did from "Revolver" and on is Definitive Classic Rock. "I Am The Walrus", "Helter Skelter", "Strawberry Fields Forever" and so on. Maybe you meant early Beatles like "She Loves You". "Revolver" was one album that helped influence all the stuff that followed
(Psychedelia and so forth).
Whatever descriptive term people want to use, Berry and Holly are CLASSIC artists, so it's Classic Rock & Roll...
Considering I spent 8.5 years at 97 Rock, I feel I'm qualified to answer this question.
"Classic Rock" as defined by the corporate commercial radio industry is effectively 1965-1989, give or take. The Beatles - Just Before Grunge.
97 Rock had a brief flirtation with "the 90's" for 1 ratings book circa 2016/2017. And it was met with criticism. It made elder Millennials and Gen Xers "feel old". "Wait, Nirvana is Classic Rock now?? ugh".
And by brief flirtation, we played 1 90's song every 4 hours or so. It was one of four options "Fell On Black Days", "Everlong", "Come As You Are" or "Interstate Love Song".
But it's not just the year of release. It's a sound thing, for better or worse.
This is just my opinion, but I detest all things 80's hair band shlock. Bon Jovi, Def Leppard, Journey, Poison, etc. Woof. All shlocky and terrible. I get those bands will still draw 40,000 something people every year forever. And yeah "huge hits". But it's just so damn cheesy. Nothing substantive in any of those songs.
80's alternative, something 97 Rock is loathe to acknowledge, is just such a better well to pull from. Tears for Fears, Depeche Mode, New Order, The Cure, REM, The Replacements, The Clash, Talking Heads, etc? SOME of that gets a spin (Burning Down the House, Rock the Casbah), but 97 Rock will NEVER play "Everybody Wants to Rule the World". I've literally never met a human who doesn't think that song isn't great.
It's a vibe thing. The men spinning Motley Crue records in high School beat up the kids that liked The Cure in high school. So, ya know, you're a ***** Low T beta cuck if you like 80's alternative rock. And the one thing "Classic Rock" can never, ever, be is not "man's man". Dumb. But true.
Some old man in 1997 decided 'THIS' is "classic rock" and 'THIS" isn't. And it's not gonna change.