3rd Seat 89 'burb

[1987SierraClassic]

I have an '89 Suburban with the third seat. I bought an owner's manual and it details a mechanism for locking the third seat in an upright position. Basically, you fold it, unlock the rear latches, pivot it upright on the front latches and use this bar to lock it there.

Does this really exist or is it one of those things that they put in the owner's manual and didn't make it to production. (I think the manual I got was an aftermarket printing)

Thanks!