Previous joint claim

Cl’s wife made a joint claim for pension credit on 1/11/22. Cl and his wife were both in receipt of disability benefits so there may have been entitlement to couple rate SDA in the calculation. Cl’s wife died on 7/11/22. Pension credit state that the joint claim was not progressed and cl has now made a new claim as a single person with three months backdating. Cl is happy with this.
My question is, could pension credit have gone ahead and processed the original joint claim with three months backdating or not?

Many thanks