According to this 2019 article in the National Catholic Register, The Marvelous Preservation of St. Bernadette, the body of Saint Bernadette had limited decay, despite:
given the close examinations, damp conditions, and normal decomposition observed of other sister buried in the same place.
The rosary she was holding rusted and her hand was not damaged until after her first wash by nuns in the chapel.
Was St Bernadette's body much less decayed than would be predicted?