I think that in general, you'll find draws and loops were used more on Golden Age guns, but like everything else associated with Longrifles, you'd be able to find exceptions. They were also utilized in a wide range of schools, but again, more so on later pieces.
I don't know if their "superior" to pins, probably a little easier to remove, and probably more of a personal taste.
The retaining pin you ask about is a pin that is driven into the stock, in the barrel channel, that goes through a slot cut in the draw. This "captures" the draw and prevents it from being fully taken out of the stock. Not sure that's explained too well, but hopefully helps.
Ed