To keep the editor as low-maintenance as possible, there is a separate program that goes through the public game files and gets all the data. It's by no means a perfect solution, but it gets mostly everything. This "separate program" also hasn't been updated in a while, so I'm sure there have been plenty of updates to the game's structure that have had the side effect of "removing" editor data that was already there. The alternative (which I myself will not do) is to add the missing bits manually. There isn't a system to merge auto-retrieved data with static data, but as mentioned previously the project is
open source and I'm happy to merge PRs.