There are two main issues with your tax letter test.docx file:
1. your five headings envisage mergefields for Description, Payment Date, Contribution, Value Received & Deductible Amount, but you only have three mergefields - for Donation_Name, Close_Date & Amount.
2. you've made a mess of the contributions layout, by using multiple tabs & spaces instead of formatting it properly with tab-stops and, in one case, a line break.
Other than those issues, the merge appears to be performing correctly.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]