That also only shows you values that have been set. There can be values that are defaulted within the program itself that can be set, but do not have their default values written to any file, so do not show up in the `defaults` command except when set manually.
Unfortunately, the usual way of finding those is to `strings` the application binary, and weed through all the chaff. And that requires either a fishing expedition, or for you to already know what you are looking for (including what binary might be responsible for that).