In this example:

Creature 1 attacks the Player

Creature 2 attacks the Player and the Player uses Improved Block

Creature 3 attacks the Playe

The extra Soak from Improved Block against what attacks is still valid?

I would say just the third attack.

Personally, i would go 2 and 3, because the improved block is used as part of the second attack, you are adding the black dice into that roll, so if that attack still succeeds the extra soak should also be applied against the damage, but I really could be persuaded either way

The OP was my exact question...and now I wonder, is there any way to get "official" rulings on these types of things?

The key phrase on the card is "After performing the Improved Block..." which does indicate that only in situation 3 (above) would the soak apply.

heptat said:

Since the block is a Reaction, it resolves before the attack lands.

So I would say it helps against attack 2+3.

I would also say 2+3. From the card text :

Special : After performing the Improved Block Active Defence , your Soak value is increased by +1 until the end of the round.

Performing the action is just using this action to give the additionnal purple Challenge to the attacker's pool. The Special effect is active before the opponent rolls his attack.

Until the end of the round (not his next turn), when he uses Imp. Block, he gets +1 Soak value -> works agains 2+3 in your exemple.

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Cwell2101 and thePREdiger, thanks for your clear explanations – really appreciate it. That makes perfect sense now