Configuring the information displayed
You can configure the columns displayed in the letter by going to Administer > CiviContribute > Payment Summary Token
Understanding how the list of contributions is created:
The payment token used in the end-of-year letters will include all contributions where the status is set to 'completed' and the contribution's financial type is set to 'deductible'.
1) If a contribution record has a non-deductible financial type but one of the line items in that contribution record has a deductible financial type, that line item only will be included in the list of donations.
2) It could happen that a contribution record was created in 2021 but the payment was only added in 2022. In that case, it is important to remember that it is the contribution's date (2021) that determines if the payment gets added to the letter or not.
3) If the contribution record is set to 'partially paid', its payments are not included in the letter. If you often have partially paid contributions, you are better off using pledges to record pledges or invoices.