In his famous exposition AGAINST Sedevacantism, Father Chazal actually articulated SEDEPRIVATIONISM.
Father repeatedly stated that the V2 Popes have no authority, that anything they attempt to teach MUST be disregarded, that the popes are impounded or quarantined. And yet they remain the visible source of unity for the Church.
By stating that they have NO AUTHORITY WHATSOEVER, he's saying that they have formally ceased to be popes but that they retain a purely material occupancy of the Holy See.
True R&R Sedeplenism would hold that those actions (teachings, commands, etc.) of the Holy See which are not contrary to Tradition still have force and must be obeyed.
That's NOT what Father Chazal holds; he holds that these actions are ALL invalid and that these Popes have formally ceased to be popes by virtue of their public heresy. He states that these men are clearly public / manifest heretics, and that there can be no doubt about this.
Without being able to ARTICULATE the formal / material distinction, Father Chazal has effectively become a sedeprivationist.