Will a severely atypical mole indicate melanoma on biopsy? I just had second incision and wait for further answers.

Would a biopsy diagnosis of a severely atypical mole indicate melanoma? They wanted to re excise again to get further margins. Wouldn't they know from first biopsy it was melanoma? Maybe this was to remove all skin to be safe. My derm said she would let me know next week. But again, cannot the first biopsy tell if melanoma or not?