I have to be honest. If Pearl Jam and the Black Crowes were out when I was a yoot then I would have no trouble calling them classic rock. Because, when you think about it: A, I would have grown up with them and I listened to classic rock, so ipso facto - they are classic rock, and B, you gotta be honest and own-up to there already being a wide variety of artists and music within 'Classic Rock'. From late '60s to, Oh, I dunno, play what we call classic rock and you will hear all manner of evolution and 'sub-genre'.
I don't know if artists like Pearl Jam are Classic Rock. I bought their first album because I listened to Classic Rock at the time, as today, and I dug it. It fit the bill. Same with Black Crowes. I bought some Tori Amos, too, and Morphine, and Jayhawks, I also had me some Joni Mitchell, the Outlaws, Rolling Stones, and some Doors.
What's so classic about Classic Rock? The format or era of existence? The groove, the band aura, the holy sh*tness of it which will make it timeless, or, classic?