Picked up a set of Bosch Platinum +2 plugs for my '01 2.0L Jetta. Application book said to use Bosch 4303. Got 'em home, pulled the old ones, held 'em up to the new ones, and saw right away that the new ones were not the right plugs. They were about 1/4" too short, obviously wrong. Did a little Googling, and by cross-referring the original NGK plug number to NipponDenso and then NipponDenso to Bosch , I found that the Bosch 4428 is the right plug -- but that's the Platinum +4 plug. Then, cross-referring the Bosch 4428 to their Platinum +2 line, I found that the correct plug is actually the Bosch 4308.
So, if you find that the Bosch App Book tells you to use a 4303, it should actually be 4308.
Original plugs had 49k on them, I was startled by how much of an improvement the new plugs made.