You're on the right track but they don't evenly rotate 90,000 songs. They drop in a few "lost gems"(or whatever you want to call them) per hour. For the most part a "music fan"(your word, not mine)would probably recognize and appreciate most of it. The masses probably would not. For one thing, it's possible to hear "adult leaning" songs back to back, say "Calcutta" followed by "King of the Road" but generally, it's a nice experience IF you occasionally like to hear something like "He's Sure the Boy I Love" and don't mind sitting though an occasional totally unfamiliar song.
Well, even with the musical knowledge and likes, even for my tastes, 90,000 songs is way over the top. I'd settle for 2000-4000 songs. But I do get yours and Big A's points. The "lost gem" idea 2-3x an hour is a good idea, but yes I know, some stations cannot do that in some markets. I get the picture guys...