Adult Disability Payment (ADP) Scotland

So I've been on a journey of ADP for 2.5 years now. Another story for another time.

My query, is backpay still a thing?

My initial application was made pre-diagnosis which got me the standard rate of daily living.

However, I got my diagnosis shortly after being awarded the standard rate, so naturally I sent in a redetermination. I got this honoured and I'm now on the enhanced rate daily living.

My assumption was that as the condition was always present. That I should be due the difference between the rates for the time between my initial application to my redetermination.

Is my assumption wrong? As they have a tendency to be.