I had a friend from Canada who was trying to get a green card. INS is able to determine whether documents are fake. The burden will be on the applicant to prove residency. If they can't they will have to go back.
Yes, they can prove documentation is fake. But will they? See, that is where the divergence is. We're able to catch illegal entrants, but pressure is placed on them to be released or look the other way. I have no reason to believe the sincerity of Washington to let the INS do its job with implementation of this new bill. IMO, it's nothing but gloss to satisfy people upset..but behind scenes they'll continue to 'encourage' people do not look too closely at these documents.
I'd love to be wrong, but they haven't earned trust. That is why many people wanted border enforcement first, myself included. To let them prove their sincerity. THEN, perhaps, measures for those already in country could be debated with some leniacy.