Nope!
If you tighten the axle nut to specifications the speedometer pickup assembly will not, and should not be able to move (rotate).
Recognizing that the tabs are there to prevent turning, they are there to prevent the speedometer pickup assembly from turning while tightening the axle.
If you can rotate the speedometer pickup assembly, your axle is too loose - dangerously loose.
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You're right.
I was thinking about the movement pre-torqued. I'll edit my post.