Magnum camshaft bearing mystery

Maybe from when the cam went in at the plant. There is nothing significant about it being a magnum engine, they all can do this or be assembled in such a rough way that bearings are damaged.
I pulled a 360 down I rebuilt over 10 years ago. I was gentle..didn't bang the cam around..but no.2 cam bearing started coming apart at the edge and working it's way toward the oil hole. Just change the one or all if you have the ability. I just changed 1,2 . 1 to get to 2 in other words.
Who knows.