Cleaning out the back of my 2002 Extreme, I noticed for the first time these four latches on the floorboard. I don't believe a third seat could fit in back there, but I don't know what should....

 

Pretty sure they are only tie-down points for securing cargo.

 

Agreed, tie downs for any cargo you may need to secure. I've never use mine and I'm coming up on 23 years of ownership.

 

Now that I know what they are I'm going to start using them right away!

 

I used to use mine quite a bit. I always keep different lengths of bungee cords back there. If I need to take gas cans to refill I will put one through the handle and secure it to the tie downs. Never know when you might need to slam on the brakes. One time I had several Rubbermaid trash cans in the back filled with fresh cut grass (no bags) taking the girl to school when this person in front of me slams on the brakes. I don't remember the details but it was at an intersection so everyone in the right lane was slowing down to turn right so we were all getting close. I hit my brakes and...the can directly behind us was forced to spill forward onto us and the center console! Yay! Just so you know I didn't drink the rest of my coffee. So after that episode I always used bungees to wrap around the rear passenger grab handles to the can handles and to the tie downs! Lesson learned.

 

Mine are a little stiff, I've been meaning to soak them in penetrating oil. Maybe it would be best to remove them first so as not to destroy the carpet.

 

Yes, remove them first.

Your carpet looks pretty nice and it is hard to find nice replacements!