Still exploring the new (to me) 2013 XF 3.0. I noticed that the 40 side of the 60/40 rear split seat isn't latched. The latch is closed so the seat won't engage when pushed back into the latch.

I read the user manual and it talks about the levers to pull to lower the rear seat but I can't find the levers anywhere in the trunk for the life of me.

Is there a secret to finding these mysterious levers?

 

Not every XF came with the folding seats, it was standard on some models and optional on others. So you may or may not have it on your XF. If you have it you should see two yellow pull handles/buttons in the boot, one on each side under the upper boot lining about half way in and about 4 inches in from each side.
If you don't have it it's a reasonably cheap and easy DIY modification.

 

If I didn't have the option then how could one of the rear seats be disengaged from the latch?

I definitely didn't see any yellow pull handles but I didn't pull back the lining very much so if it's up under there I'll have to look harder.

 

You don't have to pull back the lining to see the handles, they are in plain sight.
So if you can't see them it seems you don't have the folding seats.
I don't know for sure but I think that cars without the folding seats still have the same latches, so maybe your "40 side" latch is unhooked somehow.
If that is the case I don't know how to fix the problem, but it shouldn't be too hard.

 

I pulled back the lining last night and found a yellow lever that, after a few minutes of playing around with a screwdriver, caused the latch to release so I could put the seat back in its correct position