If you received a notice from the IRS, you must respond by the date in the letter.  If you have passed the deadline, you can call the IRS and see if you can still send the information (ask for an extension) which they usually grant but they are not required to do so.  Get the requested information to them as soon as possible and even if it is too late this year, know that you will probably have the same issue for 2017.  Go to Form 886-H-DEP for a form that may be helpful.