The context of the Merge Field of Annual Statements is from the Contact Object. This is in comparison to Receipts that are from the Payment Txn Object.

The best way to test/check is by:

• Creating a test Annual Statement Campaign. Make sure the "Statement Letter" is linked to your "Letter" record.
• Adding a single Contact to the Campaign
• Running the Annual statement process for the initial PDF generation. (Note, this is only required once as it saving details such as time frame etc. onto the campaign. If doing subsequent previews, you can skip this and the above steps)
• Click into the Campaign Member
• Press the "Annual Statement" button to preview. If you cannot see this button, then make sure you have clicked on the Campaign Member and not the Contact. If you still cannot locate, ask your Salesforce Administrator to add this button to the Page Layout.