Why is Optronics Light part # STL16RB 7 Function and # STL17RB 8 Function

I purchased a tail light a few weeks ago and thought it was a pair, I need to purchase the other side, can you help me find it. I purchased STL16RB which is the passenger side, need the driver side, the link seems to send me to STL 17RB but that says its a 8 function and the other side says 7 function. Thanks

asked by: Mike