When you draw an action card you resolve it like this:

1. Special effect

2. Spawn the left arrow

3. Spawn the right arrow

4. Move GS

What I can't figure out is if say I play a "claw" GS doe to this card, does the pile with this newly played GS move? Or is it just the "old" GS that moves?

Every swarm moves as a whole, as long as it contains at least one symbol that's been activated by the Event Card.

Hope that helps.

Okay. I'll just play it as the newly moves. As in placing the new ones and then those hordes moves. Thanks.

Okay. I'll just play it as the newly moves. As in placing the new ones and then those hordes moves. Thanks.

That's correct, it doesn't matter if the genestealer was "freshly spawned" or stayed on the formation for some rounds. The swarms just move as long as they're activated.