Back in the olden days, most people in the United States bought their magazines on the corner newsstand. Newsstand owners wanted to make sure they had the latest issue of each magazine, and so an agreement evolved between the newsstands and the publishers. Publishers would date their magazines with the date of removal on it, which also told the newsstand owner the date that the new issue was supposed to arrive.
Let's take an actual example. Got a copy of this week's Time or Newsweek on you? Note that the date on the issue is February 7, 2005, even though today is only February 3rd. The date isn't the week the issue was released; instead, it represents the date on which newsstand owners are supposed to stop selling that issue, because the new one is scheduled to arrive on that day. A monthly magazine would therefore put next month's date on it; so in the month of January, newsstands would be selling the February issue of Super Potato Tales or something like that.
Now, while this system works fairly well for news magazines and other weekly magazines, you can see that things are different for monthly magazines, such as the current genre fiction magazines. Unless every monthly magazine releases its new issue on the first of the month, the newsstand owner doesn't know exactly when to remove it. So the owners would usually wait until the new issue arrived, and then take away the old issue.
But what happened to unsold magazines? Newsstand owners didn't want to be left with a pile of unsold, out-of-date magazines, so publishers agreed to take back any of the unsold ones and give the newsstand owners credit towards future issues. While this meant that the newsstands weren't going to lose money if an issue didn't sell, the publishers would. Therefore, it was in the publisher's best interest to see that each issue stayed on the newsstand for as long as possible.
So one day, the publisher of Super Potato Tales (SPT) had an idea. (I'm making that title up; I don't really know who was first.) What if he dated his issues two months in advance instead of one? If he released the March issue in January, then it would stay on the newsstand for two whole months, giving it a chance to sell that many more copies. And so began the custom of dating issues more than one month in advance. After all, as soon as Super Potato Tales did this, the other publishers saw what they were doing and followed along.
The system fell apart, however, because newsstand owners aren't idiots. If I own a newsstand, and receive the March issue in January, I'll put it out for sale -- until the next issue (dated April) shows up. That's the signal that it's time to replace the old issue. And since publishers are dating everything two months in advance now, it may mean that I'm selling the Aprl issue in February, but why not? Whatever's the current issue is what goes on the stands. The previous issue gets sent back for credit.
Those newsstand owners who did keep both the March and April issues on the stand througout the month of February discovered that their customers weren't idiots either. Customers generally come looking for the latest issue of the magazine; it is the rare customer who hits his or her head on the last day of the month realizing they forgot to pick up this month's Super Potato Tales.
Despite this flaw in the new system, publishers still liked the idea of a date two months in advance. And so they kept up the pretense, which creates the bizarre scenario of a December Super Potato Tales filled with Christmas stories that is available for sale in October. By the time the holiday itself rolls around, SPT is already at its February issue.
So why did my April Analog arrive in January? Well, I have a subscription. The April issue has to be published in time to reach the newsstands in February. This means printing it in January. And once it's printed, there's no good reason to hold onto the subscriber copies, so the publisher just sends them out. As a consequence, subscribers will often get their issues a week or two before they show up on the newsstand.