Normally you measure the arrow from the nock (so, where the string is placed) to the end of the shaft. If you want to have a 29" arrow, the shaft itself has only about 28,5" cause the distance between the shaft and the nock has to be added.
But what if you order a bare shaft (which comes without a nock) at full length. If they say 31" does it mean that this shaft would be ca. 30,5" or do they actually have 31", so that my arrow would be 31" + ~0,5"?
What happens if a shaft has a nock attached from scratch? Are they measured from the bottom of the groove to the end of the shaft?