I don't know which country you live in but in the UK if it has the Bumeister sound system then it is premium / premium plus ( or was ) and therefore your sat nav doesn't need an SD card and is instead part of the comand system and stored on the hard drive.
My GLC premium plus is 3 years old at the end of this month and I had the maps updated yesterday to current 2020 version 14 which is the last available free before end of warranty.
My GLC premium plus is 3 years old at the end of this month and I had the maps updated yesterday to current 2020 version 14 which is the last available free before end of warranty.