My dad has been on PIP/DLA and ESA/Incapacity for work for around 15 years now. I believe the ESA is a joint claim with my mum. My mum has been receiving PIP for about 6 years now. They received a letter to migrate over to UC recently, after ringing Citizens advice they were told that it seems like they are entitled to SDP as no one receives carers allowance for either of them. They called the DWP and filled in an application which they reviewed and awarded them SDP so they have the transitional element for when they migrate over. However they have only back dated it to the time they filled in the application even though they have been entitled to it since my mum has been receiving PIP. The reason for not backdating further was because they said they didn’t inform them when my sister moved out in 2011. This is over 14 years ago, is this a valid excuse? And is there any point taking it further? I’m sure they have been asked in the past 14 years who lives in the household and they have updated them during applications for benefits and social funds etc.