The vent has nothing to do with filling. All Darts up until the carbon canister system was implemented use the same vent "system."
The vent is a simple 1/4" fitting, welded into the top area of the filler pipe up high under the top of the quarter panel. From there a short hose connects to a tube, which goes up about as high as possible, makes a "U" and turns down along the filler tube, through the trunk gasket, and "open" ends inside the rear frame rail. THAT IS the vent
When you are filling a tank, the fill depends on air being expelled up the filler as fuel goes down.
1--Some stations use way too much nozzle pressure, which aggravates the problem
2--If you are in an area that use the booted vapor recovery nozzles, these may be a problem
3--Only other cause I can think of is something wrong down at the filler entrance, IE the tank is made improperly, or a repop filler is too long, and somehow makes a protrusion into the tank which traps air
There's one station in town that I no longer EVER go to, for any of my cars. The two I "like" I leave the nozzle on the middle "latch" so it's not a really fast fill, but at that station, it never spills. Also, that particular station has the lot and the pads around the pumps in such a way that I can usually pull through to the last "leaving" pump, and "dangle" the front of the car downhill a bit. These pumps never spill, and I never top it off. I simply allow the pump to shut off on the "first try."