Income Support - Anytime Revision Possible?

Hi all,
Hoping to get abit of guidance and direction.
Can the DWP revise earlier FTT (IS) entitlement /o/p decisions when a later FTT (HB) entitlement/op was successful. 
Context
1. Alleged cohabitation case
2. (IS) O/P period 2013-2016
3. (IS) FTT was heard in 2016 and Appellant lost
4. (HB) FTT was eventually heard in 2021 and Appellant won and entitlement reinstated from 2013 - 2017 when circumstances changed

The latter Tribunal was a more thorough, with day long hearing, with the benefit of better preparation and supportive evidence. 

Any guidance would be kindly appreciated

There are no circumstances in which the DWP can revise a Tribunal decision. This is for constitutional reasons and we really ought to be glad of it in the round.

A Tribunal decision can be superseded including where it was based on a mistake of fact or ignorance as to some fact (reg 6(1)(c) D&A 1999) which could perhaps be applied here, however I am not sure that is helpful as a supersession on this basis is only backdated to the FtT decision date where it is adverse to the claimant (reg 7(5)).

I suppose you could perhaps ask the DWP to write off the debt on the basis of the new FtT’s decision, although on the other hand they may not be impressed by what is essentially a collateral attack on the 2016 FtT decision by reference to a different FtT decision in a case to which they were not party.