Recordings by Sir Elton John, Aretha Franklin, Nirvana, Eminem and thousands more were destroyed in a fire in 2008, according to a New York Times report.
They were lost when a blaze swept through a warehouse at Universal Studios Hollywood, causing extensive damage that was downplayed at the time.
In confidential documents issued in 2009, Universal Music Group estimated the loss amounted to 500,000 songs.
"Lost in the fire was, undoubtedly, a huge musical heritage," it added.
In a statement on Tuesday, UMG acknowledged the fire had been "deeply unfortunate" but disputed the New York Times' reporting.
"The incident... never affected the availability of the commercially released music nor impacted artists' compensation," it said.
"The story contains numerous inaccuracies, misleading statements, contradictions and fundamental misunderstandings of the scope of the incident and affected assets."
According to the New York Times, the recordings housed at Universal Studios spanned decades of popular music.
They included songs by Ray Charles, BB King, the Four Tops, Joni Mitchell, Al Green, Eric Clapton, the Eagles, Tom Petty, REM, Janet Jackson, Guns N' Roses, Mary J Blige, No Doubt and Snoop Dogg.
Many of the recordings were master copies - the studio tapes from which new generations of CDs, vinyl and digital copies can be generated.
Archivists will now have to rely on second-generation copies of the originals, with a resultant loss in fidelity.
Following the article's publication, REM said they were "trying to get good information to find out what happened and the effect on the band's music, if any."
REMHQ is receiving inquiries from many people concerned about the New York Times article on the Universal Music fire 11 years ago. We are trying to get good information to find out what happened and the effect on the band’s music, if any. We will detail further as and when.— R.E.M. HQ (@remhq) June 11, 2019
The fire started after overnight maintenance workers used blow torches to repair the roof of a building on one of Universal Studios' many movie sets.
Although they followed protocol and waited an hour for the shingles to cool down, a fire broke out shortly after they left.
Flames eventually reached a warehouse known as Building 6197, which housed archives of TV shows, film reels and sound recordings owned by Universal Music Group.
Though the fire was widely reported at the time, the head of Universal Studios, Ron Meyer, said there had been no major losses.
A contemporary BBC report said about 40,000 to 50,000 videos and film reels had been damaged in the blaze and that duplicates were kept elsewhere.
In its statement, UMG said it was proud of its efforts in music preservation and listed various initiatives it had spearheaded or supported.
It also referred to unspecified "constraints" that stopped it "publicly addressing some of the details of the fire."