Client used to be in receipt of IS based on incap for work since 2005. Failed PCA, decision dated 10.2.09. Appealed unsuccessfully. Tribunal decision dated 21/5/09. No full decision requested.
Client was in receipt of DLA MRC from 2005. Award from 19/7/07 to 18/7/12 was looked at again (seems to have been on DCS’s initiative, bec of failed PCA). She was then awarded HRC from 25/2/09 until 18/7/2012, with a decision dated 6.6.09.

Client first contacted IB on 11.6.09 to tell them of DLA decision. She was eventually told on 25 June to write to tribunal to have decision ‘struck out’. She wrote to tribunal and to IS/IB in June and July, but no reply.

I think it would have been possible to claim backdated IB on 11 6 and still get the linking period, which was not done because of bad advice from DWP. Is there any way to make a new linked claim now?

And could the DWP still supersede the tribunal decision based on new evidence, the DLA decision dated 6.6.09?

The highest rate care was only awarded with effect from 25.2.2009, but the tribunal was restricrted to looking at the facts as at the date of the IB decision, a fortnight earlier, and could not possibly have taken it into account to award IB on the special exemption rules even if the information had been known at the time.
It may not even have been persuasive evidence that the claimant was incapable of work at the date of decision, since unless the claimant falls into an exempt category the PCA has to be applied to him and not every condition leading to an award of HRC will make a person incapable of work. If it did, there could be no place for the special severe disability element of working tax credit that can only be paid to a person who is getting HRC.
This is surely a case for a supersession back to the date of award by the department for a change of circumstances.