Both groups were created by German record producer Frank Farian. He used the same vocal practices with both groups.  Farian got away with it, in the 1970s.

The group "Boney M" was originally just Frank Farian singing in a deep voice, backed up by himself singing, overdubbed, in a falsetto chorus. When one of his songs became a European hit, Farian hired performers to "front" the group on television: Jamaicans Liz Mitchell and Marcia Barnett, Maize Williams from Montserrat, and Bobby Farrell from Aruba. And, while the lineup changed through the years, it was well-known that Farian still sang all the male leads in the studio, and Maize Williams didn't sing on the records at all, "since her voice wasn't suited for this kind of music" (producer Farian's words).

So, only two members of the group sang on the records, although all four members sang on-stage, in concert. And, the band's concert sound was further enhanced by backing vocalists.

Numerous sources state that this was a common practice within the disco genre, and no one really cared in the 1970s...unlike when Farian did the same thing with Milli Vanilli in the 1980s.

Milli Vanilli quickly became one of the top pop acts of the late '80s, until it came out that Fab Morvan and Rob Pilatus did not sing the songs.  Both were model/dancers that Frank Farian had found in a Munich, Germany dance club.

The vocals on the Arista Records album "Girl You Know It's True" (1989) were sung by Charles Shaw, John Davis, Brad Howell, and twin sisters Jodie & Linda Rocco.  And, just like "Boney M" fifteen years earlier, producer Farian believed his vocalists lacked a marketable image. Hence, Rob and Fab on the album cover! This time, however, the record-buying public cared.  A LOT!

In the video above, Rob & Fab "lip sync" at the 1990 Grammy Awards...

Rob and Fab's grammy was revoked in late 1990, when the truth could no longer be deinied. An album with the duo's picture on the front, featuring their actual voices, was a dismal failure. In 1998, on the verge of a comeback tour, Rob was found in a German hotel room, dead of an apparent drug overdose.  Fab continued to pursue a solo career, with little notice.

"Boney M" & "Milli Vanilli"

What a difference a decade makes!