On the vpn-single-record page, there is a thumbnail of the page image. If the user clicks on that, then jquery launches a new URL in the "popup window" and thus adds the URL of that image to the history list. The "Back to Previous Page" link at the bottom of that page had a simple history.back() invocation. If the user has displayed the large page image, then they back button takes them to the page image and not the search results page.
So, on the vpn-search-results page I added a line of php to create a cookie vpn_search_results_url with the URL of the vpn-search-results as the value.
The vpn-single-record page has php which tests for that cookie. If the cookie has a value then the href on the Back to Previous Page button is given that value. If the cookie has no value displays a text warning to the user and lets them link to the search database page. So, for people who turn off cookies, they at least get a notice and a hard link to the search query form page.