You are confusing the aircraft registered serial number with the base/unit code which is displayed on the tail. The base/unit code will change if the aircraft is reassigned to a new unit, the aircraft serial number is assigned during manufacture and stays with the aircraft for life.
Link to website on French aircraft
here. Specific link to FAF aircraft
here.
Aircraft Serial Numbering System(s):
French Air Force aircraft carry French military serial numbers which are usually based on the manufacturers construction number for the airframe concerned. There is thus no overall numbering sequence, but a numbering sequence from 01 or 1 for each individual type. For example, MS.760 Paris 92 shares the same number as N.2501 Noratlas 92.
Unit/Base Aircraft Code System(s):
Most AdlA aircraft carry tactical code numbers of the form xx-AA, eg: Mirage 2000D 3-XE, where the first number denotes the Escadre (Wing), the first letter indicates the Escadron (Squadron) and the second letter denotes the individual aircraft.