Rider back refers to the back design and 808 is the stock and finish. This a poker 808 is also a bike rider back. I'm sure most of it is just marketing these days. Over the last 120 years or so the United States Playing Card Company has been buying up just about every other card company in North America. So way back in the day their may have been more of a difference in stock and finishes but these days it is getting harder and harder to tell.
Currently USPCC has two different presses(last I heard) and four different quality control standards. As for stocks available? I'm really not sure but I doubt it is more than a handful. You can feel a sleight difference in Bike, Bee, and Tally Ho brands when you compare them head to head but it might take a while to appreciate it.
I have yet to try out the 909 or the 809s so I really don't know if they are much different that the 808 stock and finish?
They're just numbers now, mainly. The 909's are supposedly Centurions, Sentinels, and Propagandas. Propagandas and Centurions are the same, with a slight finish difference in regards to Sentinels.
And there are differences in bee decks. They feel softer, smoother in the long run, and when you dribble them, it's a lot smoother. So.. softer, smoother versus the somewhat stiffer and rough-edged Tallys and Bikes.