No prob - happy to help. I'm doubtful that the firearm seller allowed for the transaction to go through without an NCIC approval #. It's more likely that the government's own systems, the checks and balances within Instacheck/NCIC, were what failed. The firearms dealer doesn't actually 'see' the NCIC report of a purchaser, they only receive a confirmation or denial of purchase  so there's not really anything to judge from their end... In regards to liability, the government is immune from any save for proximate causation which isn't really an argument here. You may be thinking of the Dylan Roof case - where his pending charges in state court should have shown up on his attempt to purchase the firearm that he used, but that one also slipped through the cracks. As a responsible multiple-gun owner myself, it's very sad and very frustrating to see the government fail in its own obligation to not allow prohibited people purchase firearms. The laws here, like in Vegas, were already in place.