Not sure it's widely known yet, but it seems turning in one blueprint at a time still might get you a dupe. For example, When coming back with 3 blueprints, I would always drop 2 on the floor and turn one in at a time to avoid getting a duplicate. But coming back from floor 21, I found that I still got 2 of the same items from 2 different blueprints this way. Bummer, but I also kinda applaud the developers for not making such an easy work around.
Unless this was patched in recently...! (cause I never had it happen in the 100 hours I've played so far)
I can confirm this is true, I got 3 BPs on my climb from 10 to 20, stored 2 on the stash and delivered them one by one. Still got duplicates.