got 15mm knuckles & want them to be 16mm?

clod, I wouldn't worry about it. If it fits, it fits. A true machinist with talent can do amazing things. Not to pat myself on the back or anything, but I've done things on a lathe that some said I couldn't do. The guy that you went to sounds like he's been doing it for a while. A good experienced machinist that's been around longer than small cnc machines knows how to get over hurdles and has probably forgotten more than the younger guys today will ever know.

Besides, he probably did use a reamer and accounted for variations in the size of the bearings. Those holes that I saw in the pics were NOT made by a simple drill bit.

I've also found that manufacturers really do like to overstate things, or make mountains out of mole hills.