The 7-month window depends on actual dates not number of days in a month. The 7-month window for July 19 is December 19 (beginning online at 8 a.m. eastern). February simply creates an issue for January at 11-months out, when start dates of January 29, 30, and and 31 all become available March 1, or at 7-months out when Sep 29 and 30 both first become available as start dates on March 1. In other words, as has become the usual case with the online system, something was wrong with the website in mentioning your 7-month out date was Dec 18. One can just count that as website glitch number 2,557,642 in the last six months, none of which are apparently ever corrected.