Backdated PIP and rules on savings

Would appreciate some advice folks.

Client has had PIP award at ERM as part of DWP reassessment of cases following court case.

Award backdated for 3 years and obviously payment of over £9000 paid. This takes them over capital limits due to existing savings.

I know that normally such lump sums are disregarded as savings/capital for 52 weeks.
Is there scope for having this disregard extended for a 3 year period???
Think there are different rules on official error???