Is 1 year too late to add new disagnoses to my case? If it's not too late, would they be given the same amount of time payable as stated in my LTD paperwork?

I am currently receiving LTD from Metlife after working for Verizon. I will only have benefits for 24 months since my issues are due to mental health. There are 2 exceptions to this 24 month rule, one is pscitzofrenia and the other is dementia. My current treatment is unleashing more symptoms that I want aware of. I have one more year before I complete my 24 month limit and I am currently being screened for Parkinson disease which is a form of alzheimers, I believe. This is because some of my symptoms for my current reasons for being on LTD are the same for Parkinson, especially the severe memory loss that I’ve been experiencing for years. Also, my mental health issues some of which include obsession and mood type disorders now may add a diagnosis of pscitzofrenia even if a mild form. My question: is too late to add these diagnoses to my case and if it’s not too late then would they be given the same amount of time payable as stated in my LTD paperwork that they would be paid until age 65?