I must be getting a little nutty - but in this craigslist ad for liberty bricks, they show a stack of them in a garage. Is that one of your original steptop papa bears there in that garage? It's kinda blurry, but that is definitely an overhanging top plate. Did the imitators do that too?
http://norfolk.craigslist.org/grd/1627091234.html
http://norfolk.craigslist.org/grd/1627091234.html