a few years back I was told by an elderly Korean lady, that those particular bows could have possibly been heavy weight exercise bows,, procurement of horn and sometimes the sinew could be far and few between ,so as not to waste good horn on bows that are for building strength and form, as far as knowing for sure- who knows.. the builders of those bows and of that time are long since dead and gone- maybe the student was to build bows from lesser materials before he was allowed to commit to using valuable horn,,, I'm no expert, but I can say for sure that that kind of bow can work to some degree, because thats how I built many before I used the first horn strips that I had when I first tried making the Korean bow.. also take into consideration that the presented bows have closed back up due to being un-used or maybe they were never opened up to start with.. the Korean horn bows real ones that I have,-have the most minimum of materials to get the most maximum of draw and results wanted,,, just because those bows have no horn doesn't mean they are any easier to build and tiller out....the particulars and finesses it takes to build them is mind blowing