There is no way to verify FUTURE income ... and that is what the Obamacare application asks people to do.
So how can you ‘verify’ income that hasn’t happened yet?
Probably the same way you are supposed to "insure" for preexisting conditions.
The problem is that IF additional income or status changes do happen and your subsidy should have been less, they’re sending you a bill ... in some cases, your change in income/status may totally disqualify you for a subsidy which means the bill could be for thousands. The IRS can use ALL of their techniques to collect this money. It’s going to be horrible for those that get these bills for hundreds or thousands of dollars.
As for your question “So how can you ‘verify’ income that hasn’t happened yet?” .... just like most of Obamacare, it doesn’t make sense. The government doesn’t care what the consequences are either, so folks will be left to deal with the IRS ... or no insurance, or no doctors, or no hospitals, or denial of treatment .... all the usual outcomes of big government interference in what should be private business/health issues.