No one could have predicted that, as her single "Rolling in the Deep" began to bubble up on the charts in January 2011, Adele would almost single-handedly provide the music industry with its first album sales increase since 2004. But by the time 2011 drew to a close, she'd moved 5.6 million copies, the most for any record in a single calendar year since [article id="1676522"]Usher's '04 set Confessions[/article] and more than the #2 and #3 albums of the year -- Michael Bublé's Christmas and Lady Gaga's Born This Way -- combined.

In the month and a half since, that number has crept to 6.39 million, according to Nielsen SoundScan. Bolstered by her latest #1 single, "Set Fire to the Rain," the album is currently enjoying its 19 non-consecutive weeks at #1, putting it just one chart-topping frame away from tying "The Bodyguard" soundtrack and Elvis Presley's Blue Hawaii's [article id="1678756"]20 weeks at #1[/article]. Should it notch a 20th week atop the charts, it will join Michael Jackson's Thriller, Prince's Purple Rain and Fleetwood Mac's Rumours on the top 10 list of albums that have spent the most time at the top of the Billboard 200 chart.

At this point, that achievement seems certain; she continues to regularly move over 100,000 units per week, so even when she's been displaced by a large-selling debut, she tends to regain her footing and the pole position quickly. She's likely to see a major sales surge this week, too, following the 54th annual Grammy Awards, where she will perform for the first time since [article id="1673944"]vocal surgery[/article] sidelined her planned U.S. tour in November and is heavily favored to take home many of the top prizes, [article id="1678825"]Album of the Year[/article] among them.

"Adele is the obvious candidate to have the biggest jump [in sales]," Billboard's associate director of charts Keith Caulfield said. "A sales surge the night of the Grammys, the week of the Grammys, is all but guaranteed for Adele."

But will it be enough to push 21 to a sales feat that hasn't been reached since Usher's Confessions in 2004 -- going Diamond with sales in excess of 10 million copies?

Caulfield thinks it is not only possible but likely. "You're thinking, 'Well, Adele's album's been around for a long time, a lot of people have already bought it, who's left to discover it? On the other hand, people keep discovering it every week," Caulfield told MTV News. "A hundred thousand people are buying the album every week, and that number is only going to grow because, believe it or not, there are people who still have not bought the album and may have heard of this woman but never actually seen her perform."

That's something that will change after Adele returns to the stage at the Grammys, and Caulfield points to the spike in sales Adele experienced after her simple, well-received performance of 21's second #1, "Someone Like You," at the [article id="1669850"]MTV Video Music Awards[/article] in late August as evidence that seeing the renowned vocalist perform live inspires people to seek out her music.

"After the awards, when she performed 'Someone Like You,' the sales surge for the single was ultimately what moved the song to #1 on the Billboard Hot 100," Caulfield said. "That one performance shoved the single to #1 before the airplay really kicked in on the song."

He added that the vocal cord problems that sidelined her this winter will only make her performance at the Grammys that much more of an event. "Whenever she performs, because it seems to be kind of a rarity and because it's been so long, because of the surgery and it's her first performance, all eyes are on Adele."

Caulfield told MTV News that not only does he expect Adele to see a substantial sales surge following the Grammys, he anticipates further singles from her album will likely keep its momentum up, ultimately resulting in her reaching the 10 million sales milestone ... and perhaps moving beyond it.

"The album has tons of singles on it," he said. " 'Rumor Has It' seems like it should be another #1 single, if they chose to release another single, that will carry her through the spring and summer. And then if they can get it to Christmas, who knows what kind of sales she could have?"

At this point, Billboard's main numbers man is betting that 21 will follow in Confessions' footsteps and join the Diamond Album Club. "I'm not going out on a limb here," Caulfield laughed. "It's Adele's 21 -- yeah, of course. It's like saying, 'Hey, do you think Madonna's tour will sell out?' Gee, I don't know, maybe."

Chaos! Profanity! Wardrobe malfunctions! Don't miss our [article id="1678706"]Grammy red-carpet live stream[/article] this Sunday, February 12, for a full three hours of mayhem, starting at 5 p.m. ET on MTV.com. And the fun doesn't end Sunday: MTV News has you covered for all the Grammy red-carpet fashion, [article id="1678701"]Grammy winners[/article] and Grammy news until the hangover wears off!