From the article in Oto Coding Alert in Feb 2020:
The last piece in the coding puzzle is determining what existing code is most similar to the septoplasty with balloon dilation. Submitting an existing reference code alongside an unlisted code is important for contextual purposes. “It is recommended that you report a comparison code of 31295 [Nasal/sinus endoscopy, surgical, with dilation (eg, balloon dilation); maxillary sinus ostium, transnasal or via canine fossa] if the surgeon uses one balloon,” advises Barbara J. Cobuzzi, MBA, CPC, COC, CPC-P, CPC-I, CENTC, CPCO, of CRN Healthcare in Tinton Falls, New Jersey. “If the surgeon uses two balloons, you should also equate 30999 to 31295, except with modifier 50 appended,” says Cobuzzi.