I don't know how it gets to an mp3, but recently, after our CD was released, this is what I found out.
The mastering guy had entered the ISRC codes correctly, but when I put the CD in iTunes, all the names, artist etc. didn't appear. That was because, as the first user, I had to enter the information in iTunes in order for CDDB to download and associate the names with the ISRC code.
From then on, everything was fine.