Replacement 68 340 four speed cams

I keep hearing what you say by regrinding a stock cam and it becomes new again. My common sense tells me, you can take away some metal, but you can not add to it. So how can you get back to stock specs? I had a 350 chevy truck that had a cam with "0" lobs on two that I replaced. I don't see how it could of been reground to factory specs, unless I wanted a "0" lift.

Don't bother on a chevy, their cams and lifters are junk. A regrind can only go so far and would be limited on lift and center with what was left on a lobe and minimum base circle.