In a strange turn of events, the top-selling Merle Haggard album on iTunes in the days immediately following his death on March 6 is a collection called 40 Greatest Hits -- containing not the original, familiar versions of the country legend’s best-known songs, but versions recorded decades later.

On the afternoon of April 7, the album was the top-selling of three Haggard titles in the Top 10 of the iTunes album chart, at No. 2, above two others containing original recordings: 20 Greatest Hits on Capitol Nashville/Universal Music Enterprises at No. 4; and at No. 9 The Essential Merle Haggard (The Epic Years) from Sony Legacy. (The 40 and 20 albums were still in the Top 10 on Friday morning.)

40 Greatest Hits is neither Haggard’s best-selling collection nor the most acclaimed. Since its 2004 release, the album -- now on the Entertainment One label, the music division of a film and television production and distribution company that acquired 40 Greatest Hits as part of its 2010 acquisition of the Compendia Music Group -- has sold nearly 120,000 copies, 7,000 of them in 2015 and fewer than 2,000 this year, according to Nielsen Music. A collection titled 16 Biggest Hits is his biggest seller since the 1991 introduction of SoundScan (now called Nielsen Music) with 1 million units, followed by Super Hits at 939,000 units. Essential has sold 203,000 copies since its release in 2004, of which nearly 37,000 were sold in 2015 and 5,000 so far this year; 20 Greatest Hits has sold nearly 84,000 since its 2002 release and 8,000 this year.

Until this week, 40 Greatest Hits had been the slowest seller among them this year, although it is the top digital seller.

So what gives? Label executives tell Billboard that it comes down to price and position on both the iTunes homepage and in its search function.

To a casual fan, the Entertainment One album would seem to be a bargain: 40 songs for $11.99, while Essential offers 14 songs for $9.99 and 20 Greatest Hits sells for $7.99. Entertainment One Nashville senior vp Van Flecher tells Billboard he believes customers are responding to 40 Greatest Hits because of “the combination of the breadth of the track [selection], the number of songs, the cool [online] package and the price.” Reps for Legacy, Universal Music Enterprises and Apple did not immediately respond to Billboard's requests for comment.

As for placement, the iTunes sales chart is based on a secret algorithm -- which includes sales velocity, sales history and other undisclosed factors -- that plays a role in the iTunes editorial team’s decisions about where to place the album in the store. On April 7, the Top 10 sales chart is the only place on the iTunes homepage that a customer would see the Entertainment One album. It was not featured in the Haggard “brick” in the carousel at the top of the iTunes homepage, although the Sony and UMG albums were; nor was it in the store’s “Hot Albums ” sliders, which featured 20 Greatest Hits.

That’s because re-recordings are a controversial topic within the iTunes store. As label or publisher contracts expire, artists can often make significantly more revenue -- as much as several dollars per album unit -- from newer recordings of old songs than they can from the originals, because they don’t have to share the earnings with the original label. Many heritage artists have released such albums. Consequently, Apple doesn’t highlight those albums at the iTunes store, because they feel they are misleading to the consumer; labels must clearly identify the songs as re-recordings (as Entertainment One did) in order to keep them stocked in the iTunes store. Even so, sources say that Apple has a policy that it will not give featured placement to re-records.

Thus, the key to 40 Greatest Hits’ success at iTunes seems to be the search function: On April 7 and 8, it was the first album to come up on a search under Haggard’s name. According to one veteran iTunes store watcher, the search function seems to rely more on sales history than sales velocity: Even though 40 Greatest Hits is the slowest-moving title this year, according to Nielsen Music, it is, however, the best-selling title in the digital format -- which is likely the reason why it comes up first in the search function.

“When an artist like Merle Haggard dies, the casual music fan says ‘I need to own Haggard,’” the iTunes veteran says. “And when they come to iTunes, they don’t look for the carousel -- they do an artist search.”

Whether or not those fans are aware -- or care -- that the songs they bought are not the original versions is unclear.