Thank you for your response.  In addition, beginning 4/2017 I began collecting long term disability from my employer's group long term disability plan.   In 2018, when I received the retroactive lump sum disability payments from both Social Security and from my employer's disability pension income (both retroactive dating back to 4/2017), I was required to reimburse my employer's group long term disability plan for the payments they had previously issued.  So I wasn't able to keep the marjority of the retroactive lump sum payment I received in 2018 from the disability pension income.  Does this change as to whether I can amend my 2017 return or is there is a way to calculate the taxes owed as if the previous year's disability pension income was actually received in the previous year?

Thank you for your response.  In addition, beginning 4/2017 I began collecting long term disability from my employer's group long term disability plan.   In 2018, when I received the retroactive lump sum disability payments from both Social Security and from my employer's disability pension income (both retroactive dating back to 4/2017), I was required to reimburse my employer's group long term disability plan for the payments they had previously issued.  So I wasn't able to keep the marjority of the retroactive lump sum payment I received in 2018 from the disability pension income.  Does this change as to whether I can amend my 2017 return or is there is a way to calculate the taxes owed as if the previous year's disability pension income was actually received in the previous year?