As the listing states
" Triumph Motorcycle Description: DUAL SEAT, L/HAUL TOURING KIT
Triumph Motorcycle Part Number: A9708164
**THIS DOES NOT INCLUDE THE BACK REST WHICH IS NOW OBSOLETE** "
These seats (A9708164) were produced and named before the Rocket Touring model existed and are for 'Standard', 'Classic' and 'Roadster' use.
They have a small square hole just behind the rider bucket portion with a plastic plug you can remove to fit the rider's backrest.
The backrest themselves (A9708160) are now considered "unobtanium" but pop up now and again - the Rocket 'Touring' version seats (T2302130) have the same backrest with a different part number (A9708158), which are interchangeable but are a slightly different colour vinyl, although the 'Touring' model seats themselves will not fit a 'Standard', 'Classic' or 'Roadster'
I have sold a used (A9708160) and a new in box one (A9708158) recently with the same seats (A9708164) that were on sale here in Australia for a similar price for the past year or two and scored another (A9708160) backrest a few days ago.
A rider's backrest (A9708158) sold recently on US eBay in April 2017 for a ridiculous price of US$405 by itself.
TRIUMPH ROCKET 3 TOURING - ADJUSTABLE RIDER BACKREST, LONGHAUL A9708158 | eBay
A few with seats to match have sold much cheaper on our forum Classifieds recently though.
I am going to see if I can modify a Corbin Fast Gun solo seat to accept it. Otherwise I will move it on to a new home too.