The licenses for some old Rock Band DLC songs are starting to expire. Some will be renewed but some won't, Harmonix explained, and the latter kind will disappear.
"When licensing songs for release for any platform, including DLC, agreements include term limits on how long the content may be sold on a given platform. This isn't specific to Rock Band - it's something that exists in pretty much all licensing agreements," Harmonix wrote on Facebook.
"Now, over five years since the release of the first batch of Rock Band DLC, we're reaching the end of some of the earliest licenses we secured. Our Music Team has been hard at work extending these licenses to make sure that this has as small an impact on the community as possible, but there may be a very limited number of songs that will no longer be offered for new purchases in the Rock Band store."
Metallica Pack 01 - "Ride the Lightning", "And Justice For All", "Blackened" - has been pulled from the Rock Band Store as a result of this.
"We'll post as more information becomes available, with re-licensing updates likely coming in on a quarterly basis," Harmonix added. "We're hard at work to minimise the impact on the RB catalogue and RB community, securing extensions for an overwhelming majority of content and, most importantly, making it a priority to give you advance notice if songs are expiring and have to come down."
Harmonix added news songs to its Rock Band Store on a weekly basis for years. 275 weeks later there are more than 4000 songs available to buy. Last week, however, was the last week any new songs will be added to the Rock Band Store.