ESA Backdate review been declined

Hello all, I have joined this forum to try to get some advice for my husband, who became totally blind at age 40 after working all his life.  He was transferred from IB to ESA (C) on 22/12/12.  He always wondered why, considering he had always worked and "contributed" that his disability benefit did not allow him to get the additional benefits such as free dental and prescriptions when others we knew who had never worked were entitled to them.  So it all became clear and seemed to make sense at last when we received the ESA3 form and letter, which we filled out to the best of our remembrance, as the last six years have been quite complicated for us.  We have just received a letter saying that he is not entitled to ESA(IR) from 22/12/12 because his partner (me) was working for 24 hours or more a week from 22/12/12).  Before we phone them, I wonder if anyone can tell us if they can see from the following whether there is any time that he would have been entitled to ESA(IR).  Thanks very much. 

1.  I was working full time on 22/12/12, but my job ended on 25/1/13 (so only 1 month of work after the transfer) and a month or two after that I starting receiving Job Seekers Allowance, which ended on 15/5/2014 (one year later). So this would have affected my husband's entitlement?

2.  In June 2013 (six months after the transfer to ESA(C)) my husband received an inheritance from his mother, so he cancelled all income related benefits and received only ESA(C) and DLA.

3.  I cannot find any paperwork before April 2014, but by that time (according to our bank statements) we were again receiving maximum Housing Benefit (so the inheritance money had gone by then).  I was still on Jobseekers until 15/5/2014, then we went to the Jobcentre for advice and I was told to apply for Income Support, and Carer's Allowance for my husband, and that he would be better off continuing to claim ESA(C) as he would get more money than if he went on ESA(IR). 
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4.  One year later, in June 2015, I returned to work, 28 hours a week, and so did not receive IS or CA, however we continued to get Housing Benefit (and my husband still had his ESA(C) and DLA).  The job was for nine months, so in April 2016 I again applied for Carer's Allowance and Income Support.

5.  So, since April 2016 we have received: My husband: ESA(C), DLA, Housing Benefit.  Me: IS and CA.   

It seems to me that there must be some times during the above when my husband would have been eligible for ESA(IR), but of course it is so confusing that I really have no idea.  I can believe it may be the case, but receiving what amounts to a two-line letter denying the claim makes me a little more suspicious.
Can anyone help please?
Many thanks for reading, and for your responses.