The sapwood is the whiter wood right under the bark, usually 2 to 4 growth rings worth then the heartwood.The early wood is the thin, corky layer between the growth rings.
I think I'd do a bend test to be sure the woods is sound. It looks like it is degrading to me. That end cut should be almost polished looking and it looks crumbly to me. Take a split off the bottom of the stave. It is waste wood anyway. Build a little test bow by getting to a clean ring on the back and a tapering the belly to the tips. Then see if it will take a good bend without breaking.