At the height of Beatlemania, skeptical journalists often asked John, Paul, George and Ringo, "What are you going to do when this is over?"

But for the Beatles, it's never been over. The band's legacy is more vibrant than ever, and the business of the Beatles will only be enhanced this year by a burst of activity surrounding the 50th anniversary of their American debut on "The Ed Sullivan Show." That Feb. 9, 1964, telecast still ranks No. 11 on the list of most-watched non-sports telecasts in TV history, with an astounding 73 million viewers.

CBS will commemorate that landmark with the Feb. 9 concert special "The Night That Changed America: A Grammy Salute to the Beatles." A boxed-set re-release of their U.S. albums issued last week is kicking off fresh promotion of the band's music that will run for years and bring new Beatles titles to the marketplace.

More than four decades after they broke up, the Beatles remain the biggest-selling band in history. With domestic album sales of 64.1 million, they are second only to Garth Brooks among the top sellers tracked by Nielsen SoundScan since the music metrics service was formed in 1991. That figure does not include incalculable millions of albums sold in the U.S. from 1964-1990; 20 of their pre-'91 titles have been certified multiplatinum by the RIAA. Their 2000 hits compilation "1" is the fourth best-selling title of the SoundScan era, with nearly 12.3 million sold.

The two surviving Beatles have been no slouches on the concert trail, either. In 2013, Paul McCartney was the No. 12 live draw in North America, according to figures from concert tracker Pollstar; his 17 stadium shows in 13 cities grossed $49.6 million. And while, by comparison, drummer Ringo Starr's All-Starr Band is a much smaller attraction, playing venues in the 2,000-seat range, in 2012, the last year Starr played a significant number of U.S. dates, his 22 shows grossed $4.2 million (ranking him No. 169 among North American tours).

In addition, the Beatles are among the biggest movers in the classic rock genre when it comes to licensed material -- from T-shirts to lamp shades to Christmas ornaments. Cirque du Soleil's "The Beatles' 'Love' " has become a Las Vegas mainstay. Homevid releases of the band's feature films, notably 1964's "A Hard Day's Night" and 1965's "Help," are perennial sellers.

All told, the band's staying power defies the gravity of a notoriously fickle business, as Beatles tunes remain a must-have item for music lovers across generations.

The value of the Beatles' catalog was reflected in the $1.9 billion price paid by Universal Music Group in 2012 for EMI Records' label holdings, which includes the band's recordings, originally released stateside by EMI's U.S. subsidiary Capitol Records. The music is now jointly released by UMG's Capitol Music Group and the Beatles' Apple Corps.

Capitol Music Group chairman-CEO Steve Barnett knows first-hand what a rarefied entity the Beatles remain. In the early 1970s, he worked for NEMS, the management company founded by the Beatles' late manager Brian Epstein.

"At this company, we all feel a tremendous responsibility to advance and protect that legacy. It's a privilege and an honor that we get to work with this incredible catalog," Barnett said. "There's a timeless essence to the music."

Ironically, Capitol initially had no faith in the commercial potential of the Beatles, even after they had already conquered the U.K. in 1963.

Historian Bruce Spizer, who will present a retrospective on American Beatlemania at downtown Los Angeles' Grammy Museum on Jan. 28, notes, "Past experience had shown Capitol that British recording artists would not do well in the United States. Add to that (Capitol A&R chief) Dave Dexter's expertise in rhythm & blues and jazz, and lack of interest in rock 'n' roll, and you can understand why Capitol did not get excited about releasing Beatles records."

Nonetheless, a confluence of events in December 1963 led Capitol to rush release of the single "I Want to Hold Your Hand," which leaped to No. 1 on the American charts. By the time the Beatles stepped on the "Ed Sullivan" stage, they were well on the way to becoming the biggest band in the world.

Capitol-EMI has been minting money off the Beatles' library ever since with an array of re-issues, live and archival releases. If there's one thing music execs can count on, it's the selling power of a Beatles record.

The latest wave began Jan. 21 with the release of "The U.S. Albums," a 13-CD set comprising the American versions of the Beatles' albums. Those collections were different in many respects (including different titles, track lineups and in some cases different takes or mixes of songs) from the versions that were released in the U.K.