This is what has me concerned about some of these aftermarket sprockets - the taper appears to be merely a lathe-turned finish, not ground, not lapped. I haven't received my replacement sprocket yet so not sure if they are all like that. But the pics of the new-style turned-from-billet sprockets all look like a dull turned finish in the hole.
The old NOS style sprockets made from a forging or casting all have a mirror finish on the tapered hole.
Again we are looking at application. In an engine sprocket we need a good solid connection to the shaft. Tool marks, such as lather turned marks will quickly loosen up as the tool marks are crushed via the load. As far as the finish on nos tapers go, the mirror look was caused from the process and tooling in which they used to gain a solid taper to taper fit. Lapping creates a dull gray, but smooth finish. The whole purpose of grinding or lapping in tapers is to obtain a metal to metal fit all over. Mating tapers cannot hold true center with each other if the contact surface between the two tapers is tight at one end and loose at the other. They will wobble. In regards to tooling, such as morse tapers, the male and female tapers give to comform to a metal to metal fit as they are joined together. Only the felmale gives if the male is solid. The tapers are what really holds the tooling together, not the tang as you find on tapered tooling sleeves and drills. The tang is only for an additional insurance against spinning one taper within the other taper, while under load. In other words, the tang on such tooling represents the nut and lock washer on engine sprocket, pinion, and crankpin shafts. Keys are used as a drive but more so as a stop to prevent taper to taper spin. On a 45 engine, the pinion gear shaft uses no key where it is attached to the flywheel. Only the tapers keep the two parts together. But...the nut and lock washer keep the tapers from loosening and spinning.