My experience has been that each knot is different, so treat it so. If you look close at the grain/growth, it "flows around knots. You can drill them out, but take care not to violate the growth/grain. Also, remember that the tension/compressional forces in the wood are most evident at the surface...on both the belly and back....so really no need to drill through either. Just ease the wood at the surface. I've had good results filling the holes with hot-melt glue. It's flexible and rubbery...and you can embellish the hole with "stuff" in the glue if you want like tourquoise dust or other gemstone pieces for example. I've filled a couple holes clear through yew that were half-inch thick without problems this way. If you are worried, leave more wood adjacent to the holes to keep enough to insure you have the strength needed....and mind where the knotholes are. In a heavier working area, this is more critical.