How does Roth know that Axl has "30 great songs stored away" that is "gonna change the face of popular music permanently and forever"?
How does he know this? I would like to think this is true. But what has Roth heard?
I'm sure it's only a sarcastic joke from Dave. It means he hasn't heard any songs, only the hype that they are great and will change the world like Wyld Stallyns did in that Bill & Ted movie. Maybe Dave reads GNR message boards?
Dave's joking that "all musicians" have those amazing songs hiding somewhere but for some reason no one has ever heard them in public. The same way like "we all" have a bestseller novel written in our drawer, or at least we could write one "if we only had time", but nobody has seen this great novel. People are saying so but there is no proof.