Our local club builder's experience is similar to Brent's. He custom specs his cams from Comp, as he's gotten lots of out-of-spec part-numbered cams from many manufacturers. He claims when he special orders they grind on a CNC rather than using old, worn-out cam grinding machines. He's see stock cams be out by 20%. Even spec'ing custom grinds he checks all cams as-received to make sure the profile meets his spec (he still has had a few out of spec).
He uses something like this:
https://www.google.com/url?sa=i&rct=...99608637978506