Just a quick post to clear up some of the confusion in this thread....
The first seats in the Model S (gen 1) were from 2012-2014.
The "Next Gen" seats (gen 2) were an option starting in the late 2014 cars.
The "Premium seats" (gen 3) were first available as an option in 2017 and then default in 2018 I believe. The distinguishable update was the adjustable headrest.
The latest car, the Palladium aka the Refresh has an all new seat as well which would technically be the Gen 4 and this started in 2021.
There may be slight overlap on some the end/beginning of model years but the timeline is relatively close. I do not believe any 2016 sold has the "Premium seat" aka the gen 3 as was mentioned in the OP. Unless the previous owner installed those DIY style you more than likely have the Gen 2 or, as Tesla calls them, the "Next Gen" seats pictured in the middle below.
Here's an image of the older three seats for visualization:
FWIW, the newest Gen 4 seats found in the new Model S is my favorite seat with the Gen 2 or Next Gen being my 2nd favorite, especially for long trips. The "Premium" seat (pictured on the right above) is fine for short drives around town but quickly becomes my least comfortable seat for longer trips. If I'm taking a longer trip I'd much prefer the first seats from the early Model S cars. I'm a larger gent and I think if you're average to below average size legs, shoulders, etc. this may not be an issue on the "Premium seat" but for me it's bad enough that it cuts of blood flow to my lower body and starts causing numbness in short order. I've driven these cars all over the country and the latest trip I took from Phoenix AZ to Northern Colorado was easily the worst trip I ever took. I was miserable. I've taken much farther trips in the Next Gen seats and felt it was one of the better driving experiences I've ever had. The first seats only become uncomfortable in the seat pan as it's rather flat and doesn't offer a lot of cushion which will make your rear a little fatigued after 10+ hours in the saddle in a day.
I know nobody asked for my Model S seat review but... there it is.