Pretty much every industry I can think of, they would keep it consistent for the customer and let the retailer figure it out on their own.
But the newspaper and magazine industry has always worked on the basis that if you can't sell it, you get your money back. It's how publishers ensure you always buy your daily paper, not the competitor, because it's always on the stands, because the retailer doesn't have to worry about overstocking. Therefore releasing you July edition halfway through June makes sense, because the retailer can't send it back until July is over, so may as well keep it out and try to sell it.
Officially they're told not to put it on sale until the cover date, but no-one enforces it, and they're sent it early enough that they'd be dumb to sit on it for so long.