Songs with multiple remixes - are they all recorded at the same time, or do they get done after a song becomes popular?

Listening to my Pandora station, I noticed that some of the songs that I’ve “thumbed up” get multiple versions played, some with pretty funky remixes. Do all these versions get produced at they same time and then one particular one is chosen for release, or do artists go back into the studio to remix songs that become hits?