What I wondered was how these acts duplicated the other guest star when they went on tour. Reason this came to mind is that I recently bought Phil Collin's solo hits on CD, and Easy Lover is botched. By that, I mean that they seem to have used a studio singer in place of Philip Bailey. Suffice it to say, the song is not the same.
In hindsight, I will guess that many stars ended up regretting having a hit with another star. Think how was Michael Jackson going to take Eddie Van Halen on the road to each of his concert stops? I will guess they had him recorded for performing Beat it live at concerts. This smacks of lip syncing though. Not so good in my opinion.