Featured Posts Dropping off after unknown date

I’m working on a WordPress theme that has “Featured Posts” on the main page. A “Featured Post” is defined by any post that the user gives a featured image. The post shows on the main page under the header with the image as a thumbnail and the header has a slider with a larger version of the image, an excerpt, and a read more link.

I have 6 posts right now that will be featured 4 of them go back to Dec 2011 the other two are from August 2011.

The problem I’m having is older posts (in this instance the August posts) aren’t being displayed.

I’m getting the id of posts inserting them into has_post_thumbnail() and if a thumbnail is attached, display it as featured:

<?php if (has_post_thumbnail( $post->ID ) ): ?>

This works… except for the date cutoff. I’ve checked the codex for the has_post_thumbnail() function, checked the theme’s functions.php and the /wp-includes/post-thumbnail-template.php pages for references to date preference and I don’t see anything.

Any ideas on this one?