Simple. You're only thinking in two dimensions. The cam grinder can grind the new lobes anywhere on that core he wants it. He moves the entire lobe in relation to the core to make up for what he grinds off. Get it? And no, there's not a thing wrong with that and it doesn't hurt a thing. The only caveat is you may need longer pushrods to make up the difference. Sometimes you do not. It simply all depends on how much he has to "move" the base circle.
