I've had quite a few of the early round boss mowers when the blade plates had to be thrown out , as there is not much support on the boss shoulder to the blade plate and the blade plate will bend easier when people misuse the mower.
A few blade plates of mine were slipping on the boss and had worn the metal thin so no matter how much you tightened the crank nut the plate would slip but I expect someone before has used the mower without tightening the crank nut enough
It looks like Victa used a larger surface area on the boss mounting face to support the larger heavier 4 blade mulch plates and made that a standard so used the same boss even if it was .a smaller oval 2 blade plate and then added the ears to the boss for more support and the ears would also stop the plate slipping but as Norm mentioned if you don't abuse your mower by smashing the blades into unmovable objects then you aren't going to notice the difference with the 2 extra ears on the boss.
The 2 ears could also be an extra layer of safety to stop the blade plate bending if someone hits something solid with the blades.
