As I have stated many times in the past, I'm no expert here. (Long-time forum members will attest to this fact!
)
Having said that, however, I did take a look at the description for O2 sensors at both pelicanparts.com and in my Bentley Service Manual (MY 1997-2004). They seem to clearly indicate the presence of 4 sensors on all models, 2 pre-cat and 2 post-cat. Have you looked closely at the Pelican Parts picture above, and closely at the exhaust arrangement on your car?