why didn't Diana And Marvin chart better

[Boogiedown]

Endless Love was indeed recorded in
separate studios in separate States. Sorry Boogiedown. Ms Ross was on tour and recorded her part after performing a show. Ditto Dreaming of you.
These days the vast majority of duets are recorded separately.

Oh dear . I really don't want to be so contrarian, Bluebrock . But here's what's in songfacts:

Getting the singers together to record this song was a challenge. They ended up meeting at a recording studio in Reno, Nevada in the early morning of May 8, 1981 following Ross' concert in nearby Lake Tahoe [[Richie came in from Los Angeles). The session began around 3:30 a.m. Less than two hours later, they had their vocals on tape.

https://www.songfacts.com/facts/dian...e/endless-love

I see nothing said either way in wiki.



Let me choose another one: Dolly and Kenny's ISLANDS IN THE STREAM , they BETTER have sung that one together, I call that duet perfection... or I'm going to go out in the surf at high tide !! lol!!