I think we are in part talking at cross purposes. To me, a ballad is simply a song, narrative or not. A broadside is a sheet of paper that bears printing. A ballad often is defined as a popular song, "especially a slow, romantic song," but I consider this just as limiting as some other definitions, such as a "narrative composition in rhythmic verse." There is tremendous overlap. I doubt we will reach agreement.

The one side-two side paper was never an issue; just wondered why the OED allows one side only to a broadside or a broadsheet while Webster's allows two sides. Americans more thrifty?.
Broadsheet, according to Webster's, is a British term for "a newspaper with full-size pages as distinguished from a tabloid," but also a synonym for broadside (OED as well). I have heard it used by printers here to refer to the large sheet of paper on which is printed the listing for a farm auction, an adv. for an entertainment, etc.