Thanks amandalouise.I'm talking about SSDI not SSI,does that make a difference?

He applied for SSDI,got approved the next month but was told there's a 5 month waiting period before those checks begin.In the meantime he did receive SSI until the SSDI began.That's what I was wondering,if he will get backpay for these months he's been waiting for the SSDI to begin since being approved.

It's all so confusing to me.I think he should just talk to them himself instead of getting me to find out for him.