ISRC CODES are needed for every CD that you publish.

ISRC CODES - find out what ISRC codes are, also where and how you get one. The ISRC (International Standard Recording Code) is the international identification system for sound recordings and music videorecordings. Each ISRC is a unique and permanent identifier for a specific recording, to help identify recordings for royalty payments. It's assigned PER TRACK, not per CD.
It stays with a recording, so that if that same recording is re-released on a different CD (like a soundtrack). it has nothing to do with the song underneath. If you (or anyone) records different versions or remixes of the same song, each track should have its own ISRC code. ISRC CODES ARE FREE. No service charge. (Unlike the UPC Barcode.) HOW TO GET ONE

International Standard Recording Code

RIAA's informational page about ISRCs: (read FAQ at the bottom