It was 50 years ago today ...

According to at least one set of global-sales statistics, Abbey Road, not Sgt. Pepper’s Lonely Hearts Club Band, is the Beatles’ most popular album. Sgt. Pepper’s is, however, their most famous. And, syllogistically speaking, if the Beatles are the world’s most famous band and Sgt. Pepper is their most famous album, then Sgt. Pepper is the most famous album ever.

Therefore, the celebrations attending Sgt. Pepper’s 50th anniversary (May 26 in England, June 2 in the United States) made perfect sense, as does Capitol’s marking the occasion with new single-CD, double-CD, quadruple-CD-with-DVDs, and double-vinyl editions, the common denominator of which is an improved stereo mix by Giles Martin, the son of the recordings’ original producer, the late George Martin.

About Giles’ version: One really can hear the difference. Whereas the old stereo mix sometimes panned instruments and even lead vocals hard left or hard right (a typical strategy in the ’60s) and therefore sounded diffuse, the new version spreads the music’s rich array of sounds and voices artfully across the sonic spectrum, giving the music a brightness, a depth, and a width that surpasses not only the original stereo mix but the original mono mix as well.

The latter, incidentally, is included on the six-disc edition’s fourth disc should anyone feel the need to compare. The second and third discs, meanwhile, comprise numerous isolated sections, flubbed takes, and trial run-throughs, most of which are pleasant if not particularly interesting.

Of greater interest is the inclusion of “Strawberry Fields Forever” and “Penny Lane” among the marginalia. Recorded during the Sgt. Pepper sessions but released separately, at the record-company’s insistence, as a double-sided single, the songs have long inspired debate among Beatlemaniacs intent on determining precisely where they would’ve fit into the album’s running order. Capitol has wisely refused to take sides, consigning both songs to the deluxe and the super-deluxe editions’ perimeters.

Another Beatlemaniac debate that the new editions won’t settle is whether Sgt. Pepper represents the pinnacle or the nadir of the music that the Fab Four made after their decision to forgo touring and to become what some would call effects-obsessed studio hermits.

Those who say “nadir” sometimes cite the lyrics, which with the exception of “A Day in the Life” exhibit a cozy whimsicality at odds with the Beatles’ reputation for witty and even revolutionary wordplay. Those who say “pinnacle” sometimes counter by insisting that, given the album’s genre-expanding instrumentation and technological innovation and the sheer charm of its most famous melodies, complaining about quaint lyrics amounts to little more than niggling. As for the many in between, they would probably say, were they honest, that their taking one side or the other (or neither) changes depending on their mood.

Perhaps more significant than the music itself is the sense accompanying its latest birthday that, from this moment on, there won’t likely be any more iconic-rock-and-roll-album milestones, no matter how elaborately festooned, worth getting worked up about. Both the Rolling Stones’ Exile on Main Street and Bruce Springsteen’s Born to Run have already had lavish anniversary treatments, and enough of the collateral arcana from Bob Dylan’s Blood on the Tracks has already come out to blunt the revelatory potential of whatever remains.

The critic Greil Marcus once described Sgt. Pepper as a “Day-Glo tombstone for its time.” Agree or disagree, it’s hard to shake the feeling that with the album’s golden anniversary an era has clearly come to an end.