This other NPR article, Classical On The National Jukebox: What's There—And What's Not, notes there are some kinks to be worked out:

"The search function is pretty cumbersome. Don't try to type in 'Gershwin' and 'Rhapsody' together, or, for that matter, artists' full names, because the site will inform you that no such recordings exist."

Also,

"For now, the only material that's included is from the Victor Talking Machine Company catalog (with materials from Columbia Records and OKeh on the way, Sony and the Library of Congress promise), so music lovers will undoubtedly find even more treasures to come. And for extra fun, users can assemble and share their own playlists."