I haven't worked for Riot since DragoRossi started up, but I did sell lots of Discos when I did.
I don't believe that they ever made a shorter Disco. They had one year in whihch they made a lower volume, kind of squashed Disco, but the hull was exactly the same.
The Disco is really the first butt bouncer, so surfing is not it's best attribute. BUT, it does have a nice flat hull, and will spin quite well for you, so it will be fun in the soup. The fins help it track a little better and get a little bit of a carve, but not much.
No matter which version it is, I'd recommend picking one up if you can get it for that cheap price. I paddled a Disco for 4 years even though Riot kept coming out with new Designs. It's really a classic design of the modern playboat era,and I loved the boat. (probably why my I paid close attention when Corran claimed that the Stinger is the \"updated Disco\")