I have been doing FCC license for 2-way radio for 20 years now. Here is my understanding. There are only designators for emissions on licensed frequencies. Since the "WIFI" bands are unlicensed, there are no designators for 802.11b,g,n,ac, etc.
If they are forcing you to use designators, I would use designators in attached pic. Will cover all your bandwidths and modulation. My experiene with the gov, is the more you throw at them the less they question you...so I would put all down and see what happens. I really do not think you are going to find a desinator for WIFI/802.11N since it is used on unlicensed frequencies and those designators are only used on FCC -LICENSE-.
