What? I have a hole in my carb? How'd that get there?

I posted about this a few years ago. A Holley 1920 for my 1969 Slant Six 225. It was the 4th rebuild carburetor I tried over 20 years and made the engine purr like a kitten instead of stumble around idle. I thought that hole was unique to the 4th carb, but can't say the others didn't have it. No repliers then had seen such or knew the reason. I thought it might be a trick the rebuilders did, but sounds like a factory thing. Not sure why they want to suck in unfiltered air. Post 14 link discusses the Carter BBS, but likely same explanation for Holley.