We have the same problem, and here is how we handle it.
We bill by the hour. At the start of tax season, we send a cover letter, mini organizer of our own design, and engagement letter. The engagement letter states that the client received an organizer, and has reviewed it to assist in his organization of tax documents, and has told us everything we ask in the organizer. The client must return the engagement letter before we start working on their return. If the client doesn't return the organizer (about 1/3), or returns a blank organizer (another 1/3), we no longer care. We are not their mothers, we are their tax preparers.
Before this, we wasted time chasing people. Now, all we need is the engagement letter. If we notice something from prior years which is strangely missing, we ask, and bill them for the time asking. If we prepare the return and they then come up with something they should have told us, they pay for the rerun. If in months or years later they tell us they forgot to include something, they pay for the amended return.
They got the organizer for free, so if we ask them for information they could have provided for free, they pay.
That said, I don't know about the Obamacare reporting requirements. It looks like if they don't answer the Obamacare questions for themselves, and all of their Obamacare dependents, It seems like the best practices is to chase the client.
Glad we bill by the hour.