See the_date() in WordPress Codex for an explanation:
SPECIAL NOTE: When there are multiple posts on a page published under the SAME DAY, the_date() only displays the date for the first post (that is, the first instance of the_date()). To repeat the date for posts published under the same day, you should use the Template Tag the_time() or get_the_date() (since 3.0) with a date-specific format string.
Use<?php the_time(get_option('date_format')); ?>to add the date set in the admin interface.