next_posts_link diving only five posts in time

Specifically, my template includes:
<nav>
<?php next_posts_link(‘↓ Older post’,”) ?>
<?php previous_posts_link(‘Newer post ↑’) ?>
</nav>

I see that, when the visitor, over and over, selects “Older post”, after the fifth post, the display returns to the first (i.e., most recent) post. There appears to be no way to cycle backward in time beyond five posts.

My blog displays one post per screen. It’s a simple-minded writing blog with a one-file template based on Jeff Starr’s H5, (Well, 3 files if one includes the requisite functions.php and symbolic CSS—the template actually links to site CSS elsewhere.)

The site is at apfwebs(dot)com

I have wp-super-cache, and have ensured the cache is refreshed… Any other advice (blog settings, etc.) would be most appreciated.