MBs don't actually hold any info. They access what is on your MDE account, so you can activate it at anytime and it will automatically link any reservations on your account. Usually no need to visit guest services, although once in a while a new band will be finicky about unlocking the hotel room.
Look at the MB as the same thing as your debit card and MDE as the bank.
The debit card itself does not hold any money. You scan it in a credit card machine and it grants the machine access to your money in the bank.
You scan your MB on a reader and it grants access to everything stored in your MDE account