Sounds like you are referring to an old version of the servicing standards - "Corrective Action Required" category has been in the last couple of editions replacing not maintained etc.
Because the corrective action is such that it may (in theory at least) reduce or impede effective function of the extinguisher, or prevent verification of the ability of the extinguisher to function (after all stored pressure extinguishers, unlike cartridge type can only be fully checked to see if they will work at the extended service or when you really need it, hence the problem with the Jewel extinguishers that are failing to function due to an internal fault you can't check for annually) or leaves the extinguisher outside legal compliance (high pressure extinguishers, i.e. CO2 where there is a statutory pressure test requirement) the standard puts a duty on the servicing organisation to put safety signage in the form of a warning sticker on affected appliances in addition to being detailed in the report.
