A dated copy of the official program page and its published questions and answers as they stood at each decision point, kept alongside any correspondence about his own case. A figure noted without the date it was read cannot later show what was relied upon.
Keep the date attached to every number
Terms published by a government can be revised, and an applicant who acted on one version needs to be able to show which version that was. Thaddeus should capture the official material each time it informs a decision, store it with the date, and file it separately from any summary prepared by an intermediary, because a summary is somebody's reading and the page is the source.
Alongside those records belongs his own arithmetic: which family members are included, what each of them adds in processing fees and in the gift amount, and the date the figures were taken. Correspondence about his individual case should be kept apart from general program material, since a notice addressed to him and a public page answer different questions and one never substitutes for the other.