ok thanks! this gives me some relief.I've had friends who graduated with me in May 2015 start up their IRTA any time between October and this past January. Small sample size, but it's likely they were accepted late as well. All depends on when a certain PI gets funding, has a previous postbac leave, or suddenly decides they need help. Keep at it!
Its not to late! I applied to the SIP program in February and didn't start emailing PI's with interest letters until a few weeks ago. I sent out hundreds of emails and just got accepted a week ago. At least 3 or so responded saying that they would have considered me but only funded IRTA interns who had plans of staying the full 1-2 years. You definitely have a shot especially if your persistent.