Thinking out loud here. Suntour, for example had a skeletonized FD cage, but the slot wasn't big enough to accommodate a chain pin (If I recall)-
I suspect that maybe Campagnolo's "hole" was just large enough to snag a chain pin, and at the right altitude (position wise) could snag a pin on a downshift or poor setup of a limiter to snag a chain. All it would take would be a few incidents, and Campagnolo (rightly so) would eliminate the fourth hole. Just guessing????
Or, it was felt to be a weak point for the too common toe clip strap snag, and was then eliminated. Perhaps the Velo-base explanation for the fourth hole elimination was pure speculation after the fact.
Shimano Dura-Ace FD that was "snagged" and bent back to stay on the road. Luckily it stayed intact. Just guessing here!