An ISRC (International Standard Recording Code) is a unique and universal identifier for a specific sound recording. It is used to track sound recording usage and sales throughout the musical ecosystem. Learn more at https://isrc.ifpi.org/en/
If you already have ISRCs for your tracks, it is very important that you use those when you submit your album's tracks for distribution because a sound recording should never have more than one ISRC in the universe (Since as stated above, it is the unique and universal identifier for a sound recording...make sense?).
However, if you don't have ISRCs for your tracks, we can provide them for you during processing.