You have to notify NAV if you transfer your TBSZ from IBKR to another investment firm. Similarly, you should notify NAV when you transfer your TBSZ from another investment provider to IBKR. In the absence of such notification, you cannot enjoy the tax protection of the TBSZ.
The data that NAV should be notified of: the fact of transfer and the amount of the transferred assets. The timeline is within 30 days from the date of the transfer.