for the record you can still get .rvz files to show achievements in launchbox. but theres some effort required. the way you get the achievements to display in launchbox is as follows: in your launchbox folder navigate to Data\Platforms and open Nintendo GameCube.xml. you'll find a ton of various information hit ctrl+f to use the find function in whatever editor you're using to edit the xml. type the name of the game and hit enter. at the bottom of each game information set you'll find
<AndroidVideoPath />
<RetroAchievementsHash></RetroAchievementsHash>
<HasCloudSynced>false</HasCloudSynced>
in this section you will add the hash listed on the retroachievements supported files tab.
so it will then look like
<AndroidVideoPath />
<RetroAchievementsHash>7ce867c45865ab18339425a3a6292cea</RetroAchievementsHash>
<HasCloudSynced>false</HasCloudSynced>
thats it. now it will show in launchbox. if it has no line for <retroachievementshash> you can safely add it. if it says couldntfilehash on this line just replace it with the hash as well. launchbox will have achievements for rvz games and they'll update properly. this doesnt just apply to rvz games either. if you have a game that retroachievements shows achievements for in your emulator but launchbox doesnt hash it properly you can use this method to get it to work correctly. its a manual method of adding achievement hashes to the xml files.