I discovered my alternator was a 2001 as was my camshaft sensor, WHY?

If it were a second hand vehicle I would have guessed the engine had been swopped out.Look at the sticker on the door pillar/door jamb, look for the production date on the decal. Look under the hood at the emission decal it will say "emission equipment equipped for 2004 model year" if it is a 2004.