From my experience in installing and upgrading Zen Cart sites, prior to version 1.5.3 (I did not use 1.5.2 because it was supposed to be for demo only) if you had an ez page that had no sort number, nor was the button changed to green, you could still put a link to that ez page somewhere and it would work.
Beginning with 1.5.3 (and possibly 1.5.2), if you do this, it goes to the index page and gives error message at top saying "Sorry, the page you were attempting to access cannot be found."
I discovered this problem when upgrading a customer to 1.5.3 and somehow found a solution was to do what it says in includes/modules/pages/page/header_php.php and comment out a line at or about line 30 as follows:
Code:
$sql = "select * from " . TABLE_EZPAGES . " where pages_id = " . (int)$ezpage_id;
// comment the following line to allow access to pages which don't have a status switch set to Yes:
//$sql .= " AND (status_toc > 0 or status_header > 0 or status_sidebox > 0 or status_footer > 0)";
That worked and I was delighted, since this customer had TONS of ez pages that were not in a sidebox, header or footer - but as links on various pages in her store.
It is nice to know that the code "fix" does not need to be applied in that file any longer and that simply clicking the TOC to green will allow the page to be displayed beginning with version 1.5.3. Now all I have to do is REMEMBER that after all these years of not having to do it! 
BTW - I noticed the problem does not apply to an upgrade to 1.5.4 I am working on right now that has Ultimate SEO URL's installed. The ez pages will show up whether the TOC is clicked green or not.
Hope this helps someone reading this thread who has encountered the same problem!