@ansonman,
In example (1) Our employer he has apparently fielded an ad, perhaps not yet published but is for some reason unsatisfied with a title he has used, so wishes to change it. The implication of 'an' is that the ad hopes to gain the attention of several different kinds of accountant, but that he's unsatisfied with just one of the titles
I could find maybe three other interpretations of (1) but hope for additional input from Man, Con, Oss, Cen, or Eng; if not Blue, Mac, FBM, Rag, or Tutov; if not rundowns on (2) and (3)