I think if the cam was down you would have other symptoms than excessive clearance.It is surprising how much lobe wear can exist and the engine still have a quiet valve train and a good idle but when the lobe is well down, if it is the exhaust you will get a regular pop back through the inlet tract noticible at first when the throttle is opened wide and as it gets worse even at idle there will be a regular popping back through the inlet.If the inlet lobe is about down the idle will still be surprisingly smooth but the cyl will miss as speed and load increases.
One thing about a worn or wearing lobe that can cause lifter noise is the lifter many times is wearing a lot as well where it contacts the cam so it shortens and gets out of self adjustment range.
Actually, wear on the lobe ramps or nose wont add clearance to the valve train and the base circle seems to not wear out at all,so it is shortening of the cam follower that gives us clearance/noise noticed with cam wear.
