Vent ribs were uncommon on field guns but competition guns such as this one were more likely to have a rib than not. At least that is what I have seen in my adventures. My first 12 ga gun was a Remington pump action that later became known as the Model 10. It was made prior to 1910 and had a rib. Same for an Iver Johnson single shot trap gun dating to the same era.
Skeet shooters seemed to be the hold outs regarding ribs, from pictures it seems it was the '20s before ribbed pumps and autoloader became most promonate.
