Why don't you copy and paste this question on a new thread? Have tried to trawl through your past posts with no success!
We will need to know what rates of DLA/PIP you were on during the time period you are talking about and whether anyone was claiming Carer's Allowance.
From what you have posted it seems that they did not assess you for income related ESA as a couple and add on any premiums that you were due so it could be that you are entitled to some back pay.
However, I did read that your OH was receiving private pensions which would be deducted from income based ESA £ for £. How much were these pensions?
So it could equally be that because of your OH's 'top up' on his move from IB to ESA it was better for the claim to be assessed as a single contribution based claim because it gave you more money. (i.e. his private pensions would be treated with 'a disregard of first £85 and the half of any remainder deducted as income per week..'). if this was the case then there would be no back pay.