What you are really doing in that page, is not really excluding 3rd party airports but, instead, excluding GSX replacement Jetway files to prevent those to exclude Jetways in a 3rd party airport, which won't work, because they are designed only to replace default jetways at default airports.
The GSX jetway replacement files include files for only those default airports that had jetways in the default scenery, if they didn't, you won't find the airport listed there, because there's just nothing to do: your 3rd party airport doesn't risk having its jetways replaced, if there's no GSX replacement file for that airport to begin with.