I believe the revised El Escorial criteria for a “clinically probable laboratory supported” diagnosis includes acute and chronic denervation in at least 2 limbs by EMG. Since you are only showing chronic denervation, you do not fit the criteria yet. Therefore, additional EMGs are not just to check for progression, but to look for acute (active) denervation. Until they find active denervation, or a spread of your UMN signs, you will most likely stay as “possible”.
I assume that a cervical MRI was done to rule out a C7-C8 radiculopathy and that the MRI was clean.