I recently asked Caleb/FFG the following question (I suspect that many experienced players may already have been aware of the answer, but since I could not find an official answer in the rules or FAQ, I thought it worth asking FFG if only to determine if there was a definitive/official ruling on it… and that the answer would be worth sharing for the benefit of other newbies).
Here is the question (with particular reference to Escape from Dol Guldur, but also with implications for other scenarios):
Here is Caleb's reply:
Only the first card revealed for the Guarded keyword is attached to that card. If the revealed card has the Surge keyword, then the next card revealed will be placed in the staging area (or resolved & placed in the discard pile if it’s a treachery).
I interpret that to mean that even if there are other Guarded objectives during set-up that yet have to have encounter cards attached to them, the card drawn from the encounter deck to fulfill the Surge keyword on a card attached to the first objective will be placed in the staging area and not on one of the other objectives. I hope this was helpful.