When adding tracks to a release on Record Union, there are 2 options available:
1) Reuse your old tracks
If you have already released a song before on Record Union, we provide the option for you to add that song in a new release. This shortcut saves you time as you do not need to upload and add information to the track again. To do this, just choose the 'Reuse your old tracks' option and type in the ISRC for the track.
Unlike new tracks though, you are not able to edit or modify any information about previously published tracks that you add to your release. The audio file will be the same, as well as the track title and all other metadata.
2) Upload a new track
This option is if you are releasing tracks on Record Union which you have not published previously.
It will let you upload brand new audio files to your account which you can fill out with new info (including ISRC's).