Question about DWB disability- prescribed period

Hi, hoping to get some advice on some aspects of this stressful and confusing process I've undertaken...

I've been filing for disability with SSA on behalf of my now 56 year old father since 2014. He has had severe mental illness for most of his life and hasn't worked since 1997. His wife/my mother died in 1993. He at one point received SSDI from approx 8/2002 until 5/2004 when they were "medically ceased." This application was done when he was inpatient hospitalized on his behalf and when the benefits were ceased he didn't follow up or appeal at all. There were other complicated issues going on at the time his benefits were terminated as well that I won't get into atm. I have been trying to ask that this prior claim be reopened based on his mental impairment at the time or that the onset date from that claim be adopted so that he can maintain his insured status. He is disabled under the same listing and he never did medically improve to the capacity of SGA (IMO)..

On this current claim he was initially approved for SSI but they have not found the medical evidence substantial enough to establish an earlier onset date for SSDI or DWB. Unfortunately, most of his older records have been destroyed at this point, including his entire past SSA file, and there was a period of time when he could not afford treatment... compounded by the fact that he has extremely poor insight into his illness and is distrusting and resistant to treatment since he doesn't believe he is sick. He is bipolar with psychosis and delusions and is very antisocial. He is collecting SSI now but his claim is currently at the Appeals Council for the issues of establishing an earlier onset date and numerous errors in the ALJ decision.

I have been going full blown detective to try to dig up any past information that I can but I was reading the ALJ decision today and something caught my eye. He was denied DWB due to the prescribed period which was calculated to begin 7 years following his wife's death, May 2000, and end in May 2007- which is still a rather distant date to gather records from. However, my dad had lost custody of me and my sister in 1998 and regained custody in 2004 at which time he became rep payee for our Survivors Benefits until we turned 18. For some reason it doesn't appear he collected Father's Benefits. I don't think he understood that he was entitled to them- he says the SSA told him our family would get a greater monthly amount if just me and my sister collected. But the SSA policy for determining the prescribed period for DWB says that it should start on the date he was last "entitled" to E benefits, which would be when my younger sister turned 16 in Sept 2007. He turned 50 in 2009 and the prescribed period would end Sept 2014, if I am correct. The SSA has already found that he became disabled in early 2014, so that would put him within that eligibility period. But I am confused if "entitled" means he had to have been collecting those benefits or just that he was eligible for them. He was collecting them at one point, they were terminated when he lost custody, and for some reason not reinstated when he regained custody.

He was also remarried briefly (less than a year) in approx 1996-1997. It seems the initial DDS used that marriage date to come up with their controlling date and prescribed period. The ALJ based it off of the date of his spouse's death.
I spoke with a rather terse woman at the local office today who said the problem was he never proved that he was divorced and it was his responsibility to do that and reapply for the Survivor benefits. But that doesn't make sense to me as he applied for benefits after that divorce and I would think it would've come up when he got benefits for his children also. They lost his file so I don't see how she would know if he provided that back in 1997. The topic also never came up in his interview for this claim or at the ALJ hearing. It was accepted that he is unmarried. I never really questioned how they calculated the dates for DWB eligibility until now, unfortunately. So I have raised this issue with the Appeals Council in writing but will just have to wait a year or however long for them to make a decision on the whole claim. It sucks that if those dates are incorrect then he is actually entitled to DWB according to the current standing decision of the ALJ.

Can anyone here clarify this issue on the prescribed period and let me know if I'm on the right track? Will the fact that he didn't claim benefits for himself but only his two kids in his care mean that they won't use that later date of my sister turning 16? And his subsequent marriage should not factor in since he is divorced, correct? Also, he may not have claimed Survivors benefits for me and my sister for the full time period of our mother's death to when he lost custody. He is not and never has been good at managing his own affairs or following through on things and he was a complete trainwreck throughout that time. Would we be able to claim that money as adults?