AFAIK, in order to apply updates and dlc to Wii U games in Cemu, you also need to install the game directly into Cemu. As a result, Cemu stores all of those games/update/dlc on the filesystem in its own directory structure, e.g. c:\cemu\mlc01\usr\title\005000e\1010af00\...
How do folks then manage those games in Launchbox? Do they keep a copy of the game roms in another directory and import those into LaunchBox? As far as my limited testing has shown that does work (Cemu will launch using the externally-selected rom, but still load the updates/dlc installed internally), but it means there are two copies of the game on the filesystem taking up space. Not a huge deal since it only affects about 30 games in my case, but I'm wondering if I'm missing something that'll eliminate the duplication.