The companies that made the rating badges sometime made rates in anticipation before they were approve by the navy. Even though so of the below rates were not approve the sailor wore them any way.
Some example of pre ww2:
Aviation Electrician's Mate was not approve until 1942. This one is pre ww2.
Aviation Gunner's Mate, this rate was never approve(pre ww2)
Aviation Yeoman never approved (pre ww2)
WW2 examples that were never approved
Officer Steward rating badge
Pt boat rating
Ordnance Battalion was approve as adistinguishing mark only
Aviation Utility was approve as a distinguishing mark only