Hi Steve
What happens when you send in additional support letters to HMCTS, they will send copies to the DWP, they will also send copies to you, they usually have a number on them so that you can add them to the bundle of documents you should have received from the DWP.
If you are unsure of anything then contact your local Welfare Rights Organisation; you can find your local Welfare Rights Organisation to help you with advice by clicking on the link below and putting in your post code, it will then come up with a MAP with a list of agencies.
advicelocal.uk Gary