Microsoft has changed the licensing structure for the different types of users in Dynamics NAV which means that Limited Users are no longer as restricted as they used to be. Now they can not only see all the data, but they also has the ability to insert data in far more tables than they used too.
Therefore, you should reconsider what type of license your users actually need. For example, if you have users who only use Dynamics NAV for time registration, there is no reason why these users are linked to a Full User License. Under the new licensing structure these users should instead be assigned to the the smaller and less expensive Limited User Licence.
Read more about the new licensing structure for Dynamics NAV