ESA severe disability premium

Good afternoon, I currently get ESA support group and PIP enhanced mobility and care benefits paid. Received a letter from DWP to say they need some further info because their records show I may be entitled to some extra money. 'Please complete form as if completing from Dec 2019 and return.' Completed form IS10 and sent back. Looking at the GOV.UK site it looks like I might have always been eligible, unless I'm missing something. Don't recall being asked about this premium before so I'm in the dark as to whether I was/am eligible for these extras. I think the 2019 date might refer to when I was placed in the enhanced PIP groups. Do you think I'm eligible ? Also live alone, council supported housing, no carers.