All these years I never noticed that outer seal.
And I replaced quite a few axle bearings. A lot of them I replace them with the green bearings so I wouldn't have noticed that anyway. But the only reason I can think there would be a seal out there underneath that adjuster or that axle retainer would be just to keep dirt out of getting into the axle bearings. Because the inner seal should keep all the rear end fluid inside the housing.
So a big thumbs up to you Rusty.