We have confirmed this is a limitation of the Tableau SDK. Tableau describes the limitation in their SDK documentation. If a Dashboard contains data from multiple Worksheets, then the resulting CSV, Excel, or Excel CrossTab file will only contain data from only the first alphabetically-named Worksheet:
Bryan Baca
A Dashboard in Tableau is a collection of data from multiple Views. When InfoBurst requests a list of Views in a Tableau Workbook from Tableau, Tableau (via its SDK) reports Dashboards as Views. If an InfoBurst user then opts to publish a Dashboard as CSV or Excel, then the result is a file with incomplete data. This appears to be a deficit with the Tableau SDK.