The description of a Dread Necromancer's Undead Mastery ability says the following:
In addition, when a dread necromancer uses the animate dead spell to create undead, she can control 4 + her Charisma bonus HD worth of undead creatures per class level (rather than the 4 HD per level normally granted by the spell).
Similarly, when a dread necromancer casts the control undead spell, the spell targets up to (2 + her Cha bonus) HD/level of undead creatures, rather than the 2 HD/level normally granted by the spell.
A (Dread) Necromancer has many ways to bring Undead under their control. From Command Undead, to Create Undead, to Rebuke, and many more. Each of these ways has a limit as to how many Undead they can command. Are all these ways of commanding undead counted seperately? I.E. can a Necromancer control an X amount of Undead through the spell Control Undead, + an X amount of Undead through rebuking them, plus an X amount of-... Etc. etc.? Or should all these methods of expanding their undead army be added together to count towards one overarching limit?