Two points: As Toomy points out, lying on the form to purchase a firearm is a felony that's never prosecuted. If that's the case, why do we need a new law? (It's noteworthy that idiot Toomy, after pointing this out, signed on to the Bill.)
Secondly. if we're going to make failing a NICS check a jail-able offense, shouldn't we make sure everybody who would fail gets notified in advance? Being a Felon isn't the only disqualifier anymore. Since the Lautenberg Amendment, a class of Misdemeanors will get you on the no-buy list. Theoretically, being a crazy person also gets you on the list. I've never heard of anybody being notified, in writing, "You are not allowed to buy a weapon for reason ____________, so don't try it."
Other than being a convicted Felon, "You should have known" is not grounds to throw somebody in jail.