THanks for the reply and that is certainly useful but the client is clear that they want the member directory page to be grouped by this State field so I need to edit members-loop.php accordingly.
Note that I am using the “reveal template” plugin to assist with the troubleshooting and even though it is outputting “page-retailers.php” as the template being used, it is simply not the case.
If I put my own test code on page.php, that will show up on the page confirming that page.php is being used.