Original: Rumors of a posthumous Nirvana box set, or anthology, first surfaced in the mid-1990s, not long after the death of the band's singer and guitarist Kurt Cobain in April 1994.
Simplified: It was the only box set by Nirvana, and it one of several albums by Nirvana after the band broke up because the lead singer and guitarist Kurt Cobain died in 1994.