Unfortunately, my husband waited to file SSA Retirement at age 74. Over the past 10 years we have been unable to complete and file our taxes due to many unforeseen circumstances (which we have since detailed to the IRS and Mass D0R). We both also thought that he would not be able to file for SSA Retirement until the taxes had been filed and that the longer he waited to file for SSA, the more he would receive in benefits - we have just found that not to be true. He filed for SSA in January, 2019 and received his payment mid February which included payments going back 6 months. Had we truly understood that he should have filed for SSA at 70 and that he would forfeit payments beyond 70, we would have filed but we really didn't know any of this. There was so much we just didn't get! We now want to appeal the back payments but are having difficulty finding someone who handles this specific type of need - most attorneys handle SSA Disability or SSI - neither of which is our need. Any advice you can give us would be greatly appreciated.
I can't recommend any specific attorney, but from what you've written I don't see any real basis for a successful appeal in your case. Not being aware of or misunderstanding Social Security rules and regulations by itself wouldn't permit your husband to claim benefits retroactively for more than the 6 months allowed under Social Security regulations. Obviously, though, I don't have access to all of the facts of your situation, so whether or not to file an appeal is up to you and your husband.
The only ways that I can think of which might allow your husband to claim more than 6 months of retroactivity would be if he previously contacted Social Security and either established a protective filing date (https://www.ssa.gov/OP_Home/handbook/handbook.15/handbook-1507.html), submitted a written intent to file for benefits (https://www.ssa.gov/OP_Home/handbook/handbook.15/handbook-1509.html), or he was dissuaded from filing for benefits sooner due to misinformation he received from an official source. The following section of Social Security's operations manual discusses what can be classified as misinformation: https://secure.ssa.gov/apps10/poms.nsf/lnx/0200204008.