Dear Benoit, cannot explain the erroneous Wiki–entry, but the French forces fighting against Austria in 1809 (Armée d'Allemagne and Armée d'Italie) did not have any corps with the numbers 5e, 6e, or 12e.
None of the sub–commands in the Army of Italy had numbers, they were known by the names of their commanders, usually with designations such as 'left wing,' right wing,' 'center' and 'reserve.'
The only numerical designations employed in the Armée d'Allemagne were 2e, 3e, 4e, 7e, 8e, 9e, 10e and later 11e (the former Army of Dalmatia).
Sources: the Army of Italy's Situations Sommaires and Situations de l'Armé d'Italie as well as N's Livrets de Situation for April–October 1809 along with other references.
Hope that is helpful.