Desktop Client: Why does the Generators dialog box not show all rows of my external Excel data?

The External Data tab of the Generators dialog box will only show the first 500 rows of data to be read in and used.

However, while only the first 500 rows of Excel data are shown, the Generator can read at least 65,000 rows. The limit is based on the number rows in an Excel spreadsheet (in Excel versions 11 and prior that limit is 65,536, or 2-to-the-16th-power; or as an Excel formula this is =2^16).