'69 Barracuda Driver's Side Door Window (Pics included)

I have 2 driver's door windows for the '69 Barracuda. One has a knob (lack of a better word) located in the lower left of the window and the other does not. Which one is correct? The part I am questioning is item 77 & 78. Does anyone have an idea of what this is for and if it is convertible specific?

Thanks,
Tom