There are times I have been lax about filling the stitch holes and have regreted it. I make fairly small holes. I usually use epoxy/wood flour, but I think I'll investigate the Durhams Rockhard putty. I used the Durhams on wood floors for many years, it is good stuff, but never really considered it for kayaks...mostly because I thought flexing would loosen it. Others appear to be using it with success. When I have missed a hole, or thought that the saturation coat would fill the hole, air was invariably trapped leaving a white, or clear, spot. Different types of wood flour make different colors of fill. Experience will help on color matching. I've never used the toothpick method. I don't think it would work well for me as I put the stitch holes very near the edge and mostly eliminate them when I round the chine. Lots of good solutions posted here. Pick those that will work for you.