Have you wondered why De La Soul is more than happy to offer its newer albums online, but has had so much trouble getting its classics (Stakes Is High and earlier) online that it gave them away at one point? You now have a good, if imperfect, explanation. Their label, Warner Music Group, tells the New York Times that its staff "don't believe it is possible" to clear all the samples in early tracks for digital music services. It doesn't explain why those samples are being held back, but the group's current sample clearance agent suspects that many of those samples may have been cleared improperly, sometimes through informal agreements. It's also possible that many of the sample deals didn't account for non-physical releases, so Warner might have to start from scratch.
The plight is a fairly common one for other artists from the '80s and '90s, when electronics enabled easy sampling before the copyright system could fully account for it. It's a minor miracle that artists like the Beastie Boys or DJ Shadow can offer their earlier work online at all. However, De La Soul faces more trouble than most. Its legendary 3 Feet High and Rising debut has over 60 samples by itself. Combine that with the high profile of many samples (Buhloone Mindstate's "Breakadawn" drew from Michael Jackson and Smokey Robinson, for example) and it could be very expensive or impossible to clear the albums.
At the same time, there's pressure to do something to get those albums on the internet. It's not just that Dave, Maseo, Posdnous and Prince Paul are losing a lot of potential revenue as the industry shifts to streaming. Like the Beatles and other pre-digital bands, it's also a matter of preserving music for the ages. What happens if and when physical albums are virtually extinct? Will people have to rely solely on pirated copies and YouTube videos to reminisce? De La Soul will have a footprint through its newer catalog (the upcoming And the Anonymous Nobody is conspicuously devoid of samples). However, there could be whole generations that don't know what made the group famous in the first place.