I've recently been notified that I have been approved to receive OAS benefits retroactive to Jan 2015. The letter did not include a T4A(OAS) for 2015 and when I phoned Service Canada the rep told me they do not send retro ones out. He said CRA will know about it. He was able to look up my file to tell me exactly how much the retro was for 2015. I have been holding off filing my 2015 taxes until this was sorted out. So even though I don't have a T4A(OAS) for 2015 should I just enter the amount as if I did?