You can receive monthly benefits while appealing the onset date. I would personally challenge the EOD, but I can certainly appreciate your concerns. You said you took a highlighter and highlighted blatant errors they made. If you can prove this, it is very possible you can get the retroactive benefits. It is very unlikely they will reverse the partially favorable. What is more likely is that they will simply reach the same decision so nothing lost or gained. You said they changed the onset date to the date on your 50th birthday. Does this result in zero backpay...not even a month or two? Plus if you win the EOD appeal, the retro activity will probably make you immediately eligible for medicare.