This 2002 set from my guess would be the Japanese version as Naruto didn't even start publishing in the US until November 2002, so I believe the 2006 set captkirk42 linked is the proper English release of the set for the scans uploaded to this set.
What I have figured out about the prefix is first 3 letters represent the set name and the fourth represents the card type so the first card that says cusc, the c represents client, which the kanji to the left of the number and the kanji in the top left of the card say. Also the reason the numbers don't start with 1 is because the continue the numbering from the previous sets so the first 7 client cards are in series 2. It also explains why there are some number overlaps in this set.