When a charity receives a portion of the residuary estate and the executor does not know which residuary estate assets will be used to satisfy the charity’s portion, here's how to report all the residuary estate assets on a charity’s Form 8971, Schedule A in BNA 706 Preparer.
All assets not specifically allocated to a beneficiary are assumed to be part of the residuary estate (unless the "Exclude From Residuary Fund (Used in the Interrelated Calculation)" checkbox is selected in the Data Entry pane for an asset).
If a charity is a residuary beneficiary (i.e., interrelated calculation), all of the assets in the residuary estate are carried to the charity’s Form 8971, Schedule A only if the charity is designated as a residuary beneficiary. To designate a charity as a residuary beneficiary, you will need to use the New (or Edit) Charity dialog. The dialog can be accessed from any row on the Form 706, Schedule O by clicking the Expanded Output icon on the "Beneficiary information" field (or via the Link Asset to Deduction feature). In the Charity List, click on the charity and click Edit to edit the charity. If the charity is not listed, click New to add the new charity. In the Edit or New Charity pane, select the “Charitable beneficiary is a residuary beneficiary for Form 8971” checkbox. The program then carries all residuary assets to the Form 8971, Schedule A for the charity.
(See also “How do I link a specific asset to a charity’s Form 8971, Schedule A?”)