It contains all of the weapons that don't come from quests, and all of the armour that is currently out the only reason you will get so many crest of alpha lupis from chest engrams is because the only available chest right now is crest of alpha lupis for Titan and hunter so the chances are if you get a chest engram it will be one of those the loot table is pretty small for three of coins meaning that there is increased chance of a duplicate