Dysplastic Nevi and graded by severity. It may take a severely dysplastic nevi years to change. No one has done a study answering that question. Please consult with a board certified dermatologist with a lot of experience in skin cancer and continue your monitoring.
I don't know how this could have happened either. If you had the biopsy done over a year ago, you then went back again in between there and no one told you anything? That is not a good sign of medical care, quite frankly. If the borders of your site were excised and sent to a lab, hopefully, they have been shown as having clear margins. Severe dysplastic nevus need to be resolved, but they are different than melanoma. But really, I think I might be looking for a new office if I were you. Some one is not on top of what's happening there and getting proper follow-up scheduled for patients.
"This answer has been solicited without seeing this patient and
cannot be held as true medical advice, but only opinion. Seek in-person
treatment with a trained medical professional for appropriate care."