There has to be some clearance in order for the wheel to fit over the hub. Otherwise, we as DIYers wouldn't be able to slide the wheel onto the hub. Is the 0.050 all around adequate? It most certainly is but may be just a little over than desired. Hard to tell with wheel manufacturers as to how much clearance is allowed and/or acceptable. Most machining practices would be to make the hub shaft tolerance +0 /-? and the wheel bore -0 / +?. Knowing what the mysterious (?) tolerance is key to a proper fitment between Hub & Bore. Is a hub-centric spacer available for a wheel bore of 66.66 with a hub bore of 66.56? I doubt it - too fragile! Most hub centric rings applicable for our wheels are listed at having an inner diameter 66.6 mm, which implies total clearance of 0.040 inches for the hub diameter. And that assumes everything is 'dead-on' otherwise, and I'm betting it isn't.

Machining practices & capabilities have improved significantly over the years. Some years back, I was in a precision machine shop doing the final inspection on an engraved calender roll (1 meter dia x 6 meters long). That same precision machine shop was performing a final grind on a US Navy submarine drive shaft and they were holding tolerances out to the 6th decimal space! (Note: Had to 'run silent' when submerged.) Hard to believe that capability existed and harder yet to believe it could be measured! Of course, the entire grinder was encased in a wooden box structure for secrecy & security.