I'm very confused

Hi everyone,
I hope this finds you as well as you can be.
I have questions about PIP backdating. Please bear with me.
71 year old man had high rate mobility DLA for years and with no review due for 10 years.
On March 4th 2024 he had a bad stroke which has left him needing a lot of care and partially blind
On advice of Social Worker at hospital I completed an AA claim form as he was over pension age and sent that off by signed for delivery post. ( Yes.... I know now that that was not correct )
Was also advised to claim Pension Credit as he would qualify once AA paid. This was made very clear on the claim form. ( it was evident he would get higher rate on both components).
Both forms stressed the urgency of the matter.
Had the nil decision on the Pension Credit within a couple of weeks and which was expected.
Never heard a thing about the AA claim despite sending reminders to process as quickly as possible.
In Oct 2024, got a claim form for PIP. Duly completed and sent off with supporting evidence.
On 18th December 2024 , had a telephone call for medical assessment and all done with support of carer.
On 16th Feb, had a text stating PIP decided and higher rates for both components awarded.
Question(s) ,
will the PIP be back dated to the date of the AA claim as no one had advised correct procedure. That would be the original change of circs indicator had someone sent it to PIP.
Will PIP be backdated due to the length of time it took DWP to process their action? We were just told to wait as there was a massive backlog.
Will the Pension Credit be reopened and backdated as PIP took so long to process? ( we've put in a new claim anyway)
He has lost out on all the heating allowances, the difference between his income and Pension Credit. The increase in his PIP which was payable from time of his stroke. He has got into considerable debt as he has to pay for help to keep him in his home.
Can I appeal against any of this? If so what?
I feel it is justly unfair that because DWP can't get their act together, people are missing out on benefits which they qualify for.
Many thanks. Stay safe and well. xx

Hiya, Thank you so much for your time and advice. It helps a great deal and gives me the option to take this forward with DWP should backdating need to be challenged. I did read somewhere ( I think 🤔) that people given incorrect advice by 'professionals' involved in a patient's care could request backdating due to that fact.
We are just waiting on the decision letter although no arrears have been paid yet which is disconcerting as I know arrears are normally paid once the decision is made and before the award letter received..
It's a very confusing, disjointed, very long winded and laborious process as you all know. I swear it's deliberate in order to put people off!. Your excellent advice and explanation has helped to clarify this situation and inspires me to continue to fight this small corner if necessary. 🤗
Have a good and restful weekend. Stay safe and well.
Many thanks again. Keep up the good work.
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