That "lobe" is to keep the bearing mount from spinning in the throwout fork. It has probably been eliminated as a cost cutting measure. Unless the bearing gets rough, there won't be much movement with or without the anti-rotation feature. Put a little high temperature wheel bearing grease in the groove to make the carrier slide freely on the bearing retainer, but don't overdo it.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!