Hi,
While at the museum, I of course spoke with staff who were knowlegable regarding the longbows. It is their interpretation that the bows were tillered first, and the nocks were added at the end, so the notches cut into the wood were from tillering the bows first. The entire tip is discolored a lighter color, which would indicate that the horn nocks were not cut through. The picture of the bow tip with the nock beside it actually shows some decay. The horn nock on display is obviously modern, and was made by longbowyer Chris Boyton. Every bowyer I've spoken with who makes horn nocks, does not cut through the horn. Two reasons: it weakens the nock, and defeats the purpose of the horn nock, which is to provide a harder material for softer woods, like yew. If you cut through the nock, the string will wear on the wood.