I know that some may not regard this as a bug, but it doesn't make much sense that the succeeded empire states are treated as still having legitimate elector counts. Marienberg, for example is a succeeded empire state at the start of the game but there is no penalty to the player's authority for attacking it.
1. Play as the empire in the ME campaign (but not marcus wulfhart).
2. wait for one of the AI elector count states to succeed from the empire (skip turns as required).
3. Opt to declare war on the succeeding state (either from the succession event that follows or declare war via the diplomacy menu at a later time).
4. Notice that there are authority penalties for destroying succeeded AI players (I think it applies a -2 malus to the player). The game still treats them as elector counts in the elector counts menu as well. In practice this slot should be grayed out or just empty.
Note the authority system may need some tweaking in general to prevent player exploits of the succession mechanic in order to avoid authority problems.