Why don't both valve covers have holes?

I know this thread is a year old. Some of the Olds engines run the PCV through the valve cover and use a breather on the other side. On my Olds 455 I run the breather then an elbow connected to the PCV valve to the carb as shown, seems too work fine. Sorry about the messy engine, I'm still working on other parts of the car. I'll be changing the M/T covers to these edelbrock covers where I want to run a breather and the PCV valve on these and need to fabricate a baffle. There is a spot for it so it shouldn't be to difficult.