The next 3 are group and sub group. 800 is body parts. 100=engine parts 200=exhaust parts 300=transmission parts 400=front end 500=rear axle 600=brakes 700=cables and shifter 900 electrical. 829 indicates a body part and rear hatch. A 98 sub group, 898 is a body repair kit.
The last three with letter and color code if needed is the part identifier. Generally if the last numeric digit is odd it is a left side part, even is a right side parts. Parts that don't care what side they go on are usually odd. For the most part a 251 829 331 B part will replace a 251 829 331 and a 251 829 331 A. And most times it is backwards compatible although you don't get any internal improvements if there were any, and that's usually why the number changes.
Greetings from Michigan's Upper Peninsula
Jeff & Jean-Marie Diebolt jdiebolt@up.net