Oil flow problem on initial prime

Your correct in your understanding of the oil flow path except you missed the part where the oil feed holes in the cam have to be lined up to the holes in the bearings that go up to the head (unless your cam has a groove in it for full time oiling and most cams don't have this groove). Their only lined up every 120 cam degrees IIRC so the oiling to the rockers only happens momentarily, not full time. So when your turning it over with the bar you'll eventually get to the point where their lined up and oil will flow.