Tim,
You don't see score marks because the carpenter was especially careful to remove them, as they would create pockets for water leading in turn to rot. On a swing beam in a barn, that's not important so you wouldn't spend the extra time.
Like I said earlier, there are a few spots elsewhere on the building where there are some axe marks -broadaxe marks, not score marks. Plus I happen to know that there would not be a sawmill in this county for a couple of decades after the time this cabin was built.
Unfortunately, the original roof is long since gone, probably replaced 100 years ago or so. So there is no telling if the split offs were in fact used for that. However, it seems unreasonable to think that so much wood would just go to waste. The settlers were a lot thriftier than all that, so much more so than their descendants.
