Yes Buddy's album was an overdubbed album, but the end result is the same:
Buddy Holly sings, the Fireballs play the music after he died.
Minnie sings, bunch of musicians play the music after she died.
No expert on this but I think that the Buddy Holly album was "overdubbed" i.e. extra music etc was put on top of the existing recordings which in that case were all sorts including studio outtakes, home recordings etc., most of them being (at the time) mono recordings. End result the "full" original recording plus extra bits to "enhance" the music.
With Minnie's album everything but the vocals were removed from the original recordings. I guess this was possible due to the fact that when she recorded them in 1978 there must have been multi track recorders in the studio with capability to lay down 24 tracks or more. After all but the vocal tracks were removed, new music and extra vocals were recorded and added in with the tempo of the songs also being changed. End result here original vocals only with everything else you hear being newly recorded.
Not sure if this album was the first of its kind. Surely Buddy Holly's "Reminiscing" album is in a similar vein in that the original music was replaced by other musicians at a later date.
Love Lives Forever is the sixth and final studio album by American soul singer Minnie Riperton.
Released posthumously, it was co-produced by her husband Richard Rudolph and released on her then-label Capitol Records. It consists of unused vocal sessions, put in music and vocally completed by artists she admired or with whom she shared her musical style. Even though most of the selections are set in a midtempo rhythm, they are calm in mood.
This album was the first of its kind, in that all of Minnie's vocals were stripped from their earlier, original music tracks and completely redone. Completed with new musicians, vocalists and arrangements. Producer Quincy Jones described this difficult project best as "keeping the bridge, but moving the water."