Today I tried updating my Volkswagen navigation to the latest available version, which can be downloaded from the Volkswagen site (in Dutch) for free, or at least for a specified amount of time after it was manufactured. Originally it used to be three years, but a blog post mentioned the updates will be available up to five years after the navigation will be taken out of production.
So I took out the current SD card from my car and made a back-up of it. Then I downloaded the correct update, unzipped it with Keka, which I downloaded just to be sure that the 7-zipped files from Volkswagen would unzip without corrupting any files.
Street names went missing after updating of Discover navigation
After I copied all of the files to the newly formatted SD card, I used Disk Utility to format it with the MS-Dos (FAT) format, I inserted it in my car and found out that the street names and road names were not showing up, but the maps were working fine.
So I did some research on Google to figure out what the hell was going on and I found out that other people using a Mac where facing the same problem. Someone mentioned an application named HiM, which can be downloaded from Macupdate, and can be used to delete hidden files from volumes created on a Mac. In my case, I simply dragged and dropped the SD card containing the navigation update into the HiM window, to delete folders like .Trashes and .Spotlight.
That did it, because after I inserted the SD card into my car, the streets were showing up as expected.
Good luck with updating your car navigation. By the way, this also applies to Discover car navigations for Audi, Seat and Skoda cars.