Pre-ordered so I had 80 packs. Opened some 1 by 1, opened a few by 5. After several packs I noticed that EVERY card was marked as “New”, even those I’d seen repeatedly. Switched to My Collection > Crafting and no capacity to Disenchant anything! Clicked around the Collection to confirm. Returned to opening packs, and the next one correctly recorded 2 New, 3 available for Disenchant. So I managed, somehow, to open roughly 25 packs with no accumulated Dust. What happened? 
Opened ~25 packs with 5 cards per pack, that’s about 125 cards. At least SOME Common cards must appear more than twice in 125 cards when there are only 145 total in the entire set.