Could be true- but would be grounds for lemon claims in most states: failure to be able to upgrade navigation maps, failure to repair software to allow feature to work, definitely impairs value.
Did you insist the work order must state "Per BMW Technical Bulletin #[ ] the upgrade feature is not functional at this time"??? I would not take the car until they documented this failure. Every month bring it back for a map update;
Interesting situation... if true
Keep it as simple as possible...but no simpler.