That's not an easy answer. Thanks to—you guessed it—money, some platforms have either gained or lost content. Taylor Swift, Prince, and other artists have seen their catalogs vanish from streaming platforms (and later reappear) due to low royalties. The issue of artist compensation has always dogged the recording industry, and it hasn't disappeared with the advent of streaming music—quite the contrary, in fact.

In some cases, you may be unable to play certain songs on demand; these tracks are only available within the scope of a themed channel. Content restrictions and missing artists and tracks are still a problem in the space, though—Swift notwithstanding—the situation has improved markedly in recent years.

Trying to figure out where things live and how you're able to access them can prove quite vexing to the uninitiated. It's one of the entertainment challenges that we face in the digital age.