>>refund claims can still be filed for tax years 2010, 2011, and 2012<<
In a related FAQ, the IRS explains that the ruling is effective 9/16/13. That means if you have same-sex married taxpayers on extension who want to file as Single for 2012, they only have until September 15. The same is true for any prior year still open.. After Sep 15 they will have to file original returns as MFJ or MFS.