[DanieLoche]

In Heroscape, unless specifically written, you never announce anything in advance.
That's one rule that is overly misunderstood by the players when activating common squads.
To be all clear :

When activating an 3-figures common squad army card (valid for any number of figures in the squad of course) :
You don't have to declare anything in advance, consequently you commit yourself in activating a specific figure only once you've done something with it. So if you move with only 1 of them, nothing stipulates the 2 others that you activated.
The Berserk Charge stipulate "same" in the sense of "same activated figures", so you are constrained only for the 1 you already move, and have the choice for 2 others. It's here only to avoid that you move for instance 6 different Dreadgul Raiders, as this army card in not designed for a swarm-like gameplay as opposed to the Zombies and Ants.

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Why this was overlooked in the power/FAQ ?
Well, simply because there's very few cases where at momentum [T] you don't want to move fig. A but at momentum [T + a dice roll] you want to ! In fact the only case I see is if due to the first move, a moved figure is destroyed (Engagement Strike or Disengage ?).
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In conclusion, if you didn't move 3 figures with your initial move but only 1 for instance, then you are free to choose the 2 additional others you may want to move with the special power. And this is the case with any other special power in common squads (swarm-like powers, etc...): never feel like you are constrained in your squad figures choices unless you already did something with the total amount of figures (here, 3 for my example) allowed.

That's my personal point of view of course as I am not part of C3V design team, but I am pretty confident in such understanding : it's the same mindset that allows you to attack with a squad figure even if you did not move with it right before.