You missed September - that's just gone off sale.
It's common for magazines to publish in the month ahead of the cover date, not least because of the psychology of someone picking up a magazine at, say, the end of August, with an August cover date, and deciding it's old and there must be a new one due out soon.
However, things do get a bit skewed this time of year by the fact we publish 13 issues each year, not 12: the usual dozen with monthly date lines, and the Awards special, due on sale in October.
So with a magazine out every four weeks, not every calendar month, things get a bit 'pulled forward' around now, then get back to normal post-Awards issue.