This wasn't exactly fun to pull out. The PO had aftermarket secondary cats welded in so it pretty much had to come out in one piece. This halfass bandaid repair relocated the downstream o2 sensors after the secondary cats, the stock set up has it located between the cats. This explains why my SES didn't start lighting up until the primary cat totally disintegrated.
I realize this is almost a year late, but information for others based on what I have found.
This is based off the information on my 2002 Pathfinder VQ35 and it may not apply or it may apply to CA models only, etc etc etc. The 2002 Pathfinder VQ35 has 4 cats just like the VQ40 with O2 sensors between each set of cats. When I took the exhaust apart the second "cats" are actually baffles and not cats at all even though everyone refers to them as "cats" but they were never and are never going to be cats...they are just baffles. In your picture the second "cats" do look like cats based on the outside casting but if they were empty I would be skeptical, YMMV.
Information to use as you wish: Anything after the last O2 sensor, the computer does not care about and in major cities in Texas if the OBDII data says it is "ok", then it is "ok".