"Module:Header template" on a given Wikisource supplies a number of parameters automatically based on an index page if they are not otherwise supplied in the <pages header=1/> tag, including "prev", "next", "current", and so on. If the page using that tag corresponds to the second link in the corresponding index's table of contents, however, then the first link is not supplied as the "prev" parameter. This results in situations such as that in this page, which according to the book's table of contents should be noted in the header as following this page but currently isn't.
I suspect that changing ">" to ">=" on line 300 of "includes/Parser/PagesTagParser.php" would address this issue.