What actually got my decision overturned at mandatory reconsideration

After two refusals I got it overturned at the MR stage rather than having to go all the way to tribunal, and looking back I think it came down to three things. Posting in case it saves someone else a year of their life.

I stopped arguing about my diagnosis and started arguing about the descriptors.

The assessment report is scored against a specific list of descriptors, and nobody at the DWP is sitting there weighing up how ill you are in general terms. Go through the descriptor list one by one, and for each one write down which descriptor applies to you and why, on your worst days rather than your best ones.

The word "reliably" does an enormous amount of work.

The regulations require you to be able to do a thing safely, to an acceptable standard, repeatedly, and in a reasonable time. If you can manage something once and then need to lie down for two hours afterwards, you are not doing it reliably, and that is a legal point rather than a plea for sympathy. Say it explicitly and quote the wording back at them.

I quoted the assessment report back at them.

Mine said I had "walked to the chair unaided". I pointed out that the room was four metres across, that I had been observed for under a minute, and that this single observation was being used as evidence against a mobility descriptor about making a 20 metre journey repeatedly. Once you put it like that it becomes quite hard for a decision maker to defend.

Happy to answer questions, though I am not an adviser and you should get proper advice from Citizens Advice or a local welfare rights service if there is one near you.