Selling a brand new (never been on the snow) seat and mounting bracket off an 18 Polaris Axys 800. It's never seen the snow, let alone even really been sat on.
From everything I’ve read they do interchange. The majority of the tank mold has remained unchanged since IQ chassis, they have massaged the front where it meets the overstructures and fuel pump locations but seat wise they remain the same. From everything I’ve seen.
That said I've never had a bracket fit right with a used tank. I'm thinking the fuel swells them. Regardless of what vintage (bracket height) it always seems to compress the back half of the tank when installing. Maybe just my myopic experience.
If you sell just the seat, I'd take the bracket, just to see if I'm full of SH!T.