According to the letter d'Erlon included in his memoirs, there was:
Paris January 7, 1831
I am pleased to announce that I have decided that you would be
put on the lists of the active officers of the army. This measure had
to be delayed because it was important to know with precision the
effects of the order of 26 August 1830 on the abolition of convictions
and decisions of the government, imposed for political actions since
July 7, 1815 and the need to consult the Garde des Sceaux (Minister
of Justice), to see and identify (evaluate political motives of judgements).
The opinion of the Minister is that, after this order and the
judgment of the Cour de Cassassion of June 11, 1825, you were back
in the fullness of your rights, and that there was no objection to see
you regain your rank in the army.
I applaud this interpretation, which gives back to the army one
of his bravest generals, and I will give orders accordingly.
Signed: Marshal Duke of Dalmatia
So candidly, I'm getting overloaded with details and am not remembering things - so I need to go piece all back together to see why d'Erlon's case took such processing time, and why Grouchy's did not, and for that matter, the balance of the officers who were put on the various lists from 1815 and 1816.