Gilbert Bohec has informed me that the Dent de Crolles system now has a thirteenth entrance - le nid de Choucas
(The Jackdaw's Nest).
It is well named as it is located high in the eastern face. It was discovered from below by scaling in the Grotte Chevalier. The photograph, taken by Gilbert from his house, has a red cross marking the new entrance. You can see the Annette and Chevalier entrances marked at the top of the grassy terrace towards the left.
I think I would have got vertigo if I had stuck my head out of there...