How EngageOne Designer handles variables in headers of transaction tables

The overflow is what happens after the entire content of the page has been rendered and EngageOne Designer determines a page break is needed. In order for the header and footer to be placed correctly at every page break, the rows for the entire table are rendered at once. Thus, when the footer and header at the page break are run, the rows which follow (on the next page) have already been calculated.
The only way to modify the values in a given row is in previous rows. Some customers have worked around this by having a layout which allowed them to predict the number of rows at which the page break occurs and incrementing a counter appropriately. You can check directly in the header if there has been an overflow using the Table page overflow and Table column overflow system variables. See the Designer User's Guide p. 77 under "Using overflow variables".
Environment Details
UPDATED:  August 24, 2017