Can an enemy card have more then one shadow card? They should get shadow cards until all enemies have 1 card (not at least 1 card). So if an enemy already have 1 shadow card I will not give it a second shadow card so the attack will have 2 shadow cards?
Usually the enemy card will specify when there is to be more than one shadow card and when it is drawn, if the encounter deck happens to run out first then no more shadow cards are dealt out because the encounter deck specifically doesn't get "reset" unless a card effect tells it to or you are in the quest phase.
For instance there are enemies that say deal it additional shadow card(s) when it attacks, if after the initial dealing of shadow cards (player order around the table) there are no encounter cards left then that enemy won't get it's extra card. Indeed if you run out of cards on the initial dealing of shadow cards some enemies won't get even one. This has saved our group several times because we can defend exactly against enemies with no shadow card and save enough to whack it in the attack window, and even have an extra ranged character to help someone else. Of course you will face the entire encounter deck starting the next quest phase