Early A Gas Caps-Vented or Non-vented?

The non-emissions A boy vents are excellent, as they are up high and prevent spillage. I've owned a 69 and 70 RR and both had the filler behind the plate. This means you MUST have an excellent sealing cap or they will leak. The A body with the high mount filler presents a natural vacuum break to stop any siphon

The disadvantage is modern pumps some of which operate at too much pressure, and the horrid emission filler nozzles, which we don't deal with here.

The tank vent has nothing to do with filling the tank, by the way. That is done by the "split level" baffle, which in some cars does not work that well. My thought is that the baffle needs to have a larger air passage and come up higher in the filler to guarantee a clear passage.

On a side note, the filler in the much-hated 95 Olds Cutlass Sierra (now gone) could be a PITA to fill at some stations, with multiple shut offs