Is there any way of adding in a missing airport at this stage, or a way for us to suggest an airport that you guys can create the entry for that we can then edit and build from there?
For the moment, no solution on your side to add an airport. So you hit the nail on the head with your second suggestion 
If possible and to help us, we need these informations :
- Official data (e.g Airnav website for USA, SIA website for France)
- Ident of the airport
- Name of the airport
- City of the airport
- Latitude
- Longitude
- Altitude
Thanks for the quick answer. Should we create a topic and post them here?
You can go on the officiel forum and create a topic. Our community team will create the bug on our side.
From the regular forums (the only reason why I’m posting here, is technically the airport exist in a form, but the identifier is wrong)
(ref; Incorrect Airport Information (53NH/ 4MB) - Airports - Microsoft Flight Simulator Forums)
53NH technically is “Meredith Bay” (Meredith, NH), a seaplane strip @ (43.652225°, -71.483750°, 503’) with a 3,000’ x 100’ water strip in a 10-28 configuration)
As currently shown, 53NH is actually 4MB Moultonborough (Moultonborough, NH), with the only physical difference is the posted runway distance being 3505’ (instead of the ~2900’ as shown in the sim)
(was practicing some loss of power conditions in the area within the sim, knowing about 4MB, and got a rude awakening when 4MB didn’t show up in the G1000 database 
)