Radiator Cap Question

[B.SUTTON]

I'm pretty sure I already know the answer to this, but here goes anyway:

The other day I came across stainless 30-31 Model A repro radiator caps being sold on ebay by a place called Classic Auto Parts Group Inc. The picture in the description was fuzzy but the 'buy it now' price was under $10 so I took a gamble. Got the part in the mail and it looks more than acceptable for the money.

-now my question: Upon flipping the cap over, I noticed that there is a small vent hole drilled in the underside. I contacted the seller about this and he informed me that 'it's supposed to be that way' since the model A has a non-pressurized cooling system. Now, maybe I'm a dope, but I dont believe that any of the other old wore out A caps I have, have a vent hole.

Is there supposed to be one???

Seems to me that when the coolant level comes up in the top tank, it's gonna escape that hole and end up on the hood.

Thanks for your insight!
-Brian