I haven't tracked down all the info yet on 2002 Finest but here's what I know.
1. Pack issued rookie autograph cards are on the checklist between #115-136.
2. They are serial numbered on the back #/1200.
3. The card # is on a gold sticker on the back.
Here's what I can tell you about the other rookies like the Walker you have.
1. The checklist runs between #151-182.
2. They do not have a serial number on the back.
3. The card number is printed on the back on the same spot the stickers would seem to be covering.
4. The front and back is otherwise identical in terms of pictures, text, etc. Both feature Topps certification stickers.
5. Each of these cards card #'s are exactly 46 higher than their checklisted counterparts (e.g. Javon Walker /w card # sticker and #/1200 is 124, the one with the missing serial # is 170.)
6. Beckett and TCDB.com do not list these cards as part of the checklist. Not does a Topps checklist that was included in the hobby box
I can only offer conjecture on these higher numbered cards. They could be ones intended as damage replacements. Topps may have planned for a larger checklist on this release and since it was smaller, added card # stickers on the back, stamped serial numbered them, then packed them out. I doubt cards like your Walker were ever in packs but I can't conclusively prove that either.