@Reacon I wish I could +1 you 1000 times. Here's how I fixed the naming issue:
All the other cars had a dlc.text file, which indicates that there is an alternate name for that car, not what the developer put in vehicles.meta
Every car has a content.xml file, which points to the .META files (like vehicles.meta and dlctext.meta) inside the data folder, to tell the game to load those files.
Also, if the developer is making the mod for multiple languages, they may include a data folder within the x64 folder of the dlc.rpf, then a lang folder with the 12 available languages (only matters for your selected language in GTA5 settings), each language .rpf has a .gxt2 file that points directly to the vehicles.meta names under makeName and gameName. It may also have the names of car mods, such as spoilers, bumpers, etc.
The problem was, my car mod didn't have a dlctext.meta or a lang folder, as the developer just wanted to stick to the names in vehicles.meta (which makes the car names confusing).
So I added a dlctext.meta file (which is the same for all car mods, you need to make sure that "hasGlobalTextFile" is set to TRUE.
Then, you need to add two things in content.xml, so content.xml knows which files need to be loaded in-game.
<overlay value="false" />
<disabled value="true" />
<persistent value="false" />
Replace NAME with the dlc name (usually folder name holding dlc.rpf, or the name in dlclist, or the other names in content.xml)
So yeah, I thank you for helping me solve this issue that stumped me a few years back. Also helped me realize that there isn't that much code between two files, helped me simplify the concept.