Advancing Cam Question

I've degreed a couple cams when I installed them. You "gots to know".

Now I'm advancing my MP 292-508 cam from straight up (108 ICL), to 104. It has a double roller chain with the 3 keyways; 4* advanced, 0, and 4* retarded. I don't know what chain and gears they are, as I bought the engine used. However, I have had the cam (and everything else) out of the engine, and checked it when I re-installed it.

My questions are: are the keyways in these gears prone to being machined inaccurately? Do I need to check and see if it actually moved 4*? I know the best answer is, "check it". But if the answers are overwhelmingly in favor of them being accurate, I'll just move it and put it back together.