Hi Carlos On top of my head I'd say documents with applied labels without a protection policy associated with are unaffected since the label is meta-data of the document. IMHO it does not matter the label is template based, ad-hoc or a regular label. However, a sensitivity labelled document with a protection policy have to be unprotected before the licence expires. You cam compare it with renting an apartment - you have to move your belongings out of the apartment before you give back the keys to the landlord.
There are several ways to do that as a bulk operation. AIP Scanner should be able to do such things. Another one is using powershell, the user should have aip superuser kind of role. Otherwise you cannot access other users data. This may be handy to just scan through folders w/o the scanner installed. You can list labels and report unprotected files. May be you are interested in this figures to control the rate of unlabelled volume of data hanging around. So estimate at what point another awareness campaign should be launched.