You may get opposing views, but I think you have two things happening with the cam:
1. The angle of the cam gear is going to push the camshaft outward and into the thrust plate when the engine is running.
2. The angle of the cam lobes is going to make the camshaft want to travel backwards when the engine is running...the lobes running against the 12 lifters, that is. The cam gear will win the tug of war but evidently not all the time...
At idle (remember your cam is only turning at 1/2 the speed of the crankshaft) the helical gear won't have anywhere near the force it has at say 1000 rpm, so your crankshaft can move in/out by the amount of clearance present. If you're idling at 425 rpm, your camshaft is only turning at 212.5 rpm. See...I wasn't asleep in all of those math classes. That can cause your ignition timing to change and also may cause your valve timing to change. The more that plate wears the more low speed change might occur. If you look at a used thrust plate, you'll see a circular wear pattern. I've seen some of these worn to around .020". That allows a lot more camshaft movement than I think is good.
By coincidence I just replaced the camshaft, gear and thrust plate in my engine. I had been suffering a wonky idle (essentially persistent misfires at idle) for a few years. They went away over about 800 rpm but none of the typical problems would fix the idle misfires. The thrust plate had around .016" gap between the camshaft. Now it idles very smoothly...as it should. One lifter is resisting rotation, but that's either a matter of break-in or something else, and I haven't yet decided what to do about it.
