Read this carefully https://www.apdaparkinson.org/resources-support...

If your SSDI claim is denied, consider contacting an SSDI lawyer who can help you navigate SSA’s rules and regulations on appeal.
My disability claim took almost 3 years to settle. It included money for SSDI from time of first file,
It seems that about 1/4 of claims go through with no problem. 3/4 are denied. More than 3/4 of thoose denied are approved after appeal.
lawer costs nothing if you lose the appeal. They only get pid if you get paid.