Expressed or Inferred Diabetes Claim from AO, Nehmer class

My father in-law first filed a form 21-526 on 8/2/2001 for prostate cancer and heart condition due to AO.  The VA has conceded that this claim remained opened from that date until 3/25/2020.  The VA conceded service connection for CAD, prostate cancer, diabetes mellitus, diabetic peripheral neuropathy, etc with an effective date of 12/20/2017.  The VA conceded on 3/25/2020 an effective date of 8/2/2001 for the CAD and prostate cancer, but denied an earlier effective date for diabetes and neuropathy.  The VA has conceded a first diagnosis date for diabetes and neuropathy of 10/3/2006.  I would like to appeal the 3/25/2020 rating decision denial of the diabetes and neuropathy to an effective date of 10/3/2006.  I am hoping to use an “expressed or inferred claim” due to the fact that the initial claim remained open continuously from 8/2001 through 3/2020, and that with an open diagnosis of CAD, that a diabetes claim was inferred.  I would appreciate any guidance on language to use, cases to refer to, and which type of appeal format to use.  This was initiated under the old system, and a Nehmer de novo review was done on 4/28/2020.  Thanks for your help!