Deductions & credits

If I paid for medical Expenses in 2019, and I did not get reimbursed until May 2020, can I assume that the expenses for 2019 are 2019 and  Expense reimbursements for 2020  are 2020 EXPENSE  COSTS!    And since I only received  a partial reimbursement that I will be able to show on my 2020 Tax return!