I hope Nisekoi's current rank in the ToC and last week doesn't affect its future too much.
I would assume that 10.15 is not the release date for this issue. We are not three issues ahead of Japan. Issue #44 comes out on Monday, #45 on October 8, issue #46 on the fifteenth. Jump does not go to press three weeks in advance, they print less than a week before going on sale. I also see that it says 10.15 on the cover, one of many dates printed. It also says 10.1 on the top left, above the magazine title. I do not speak Japanese, and can not explain what the 10.15 refers to. Since we do not get issues three weeks in advance, and Jump is not taking two weeks off, assume that 10.15 is not the street date for issue #44
i.e. on sale: Monday (1. Oct.), published for: 10/15/2012
If you're wondering about the difference in time, well that's just how the publishing industry works. It's nothing unusual. You can easily think of dozens of examples: take some TV guide (sold long before the time frame it's covering) or even your daily newspaper which can be bought several hours before the new day...
The timely difference tends to get bigger with the publishing intervals. (Like, daily newspaper = just a few hours; weekly journal = several days/weeks; monthly mag = several weeks/months)
Sticking with other examples from Shueisha manga anthologies: the October issue of Ultra JUMP went on sale 9/19, October issue of JUMP SQ had an official street date of September 4th and some guys had their copies already at hand in late August.
And you'll be most certainly able to get your hands on the February issues of most monthly magazines in late December. (Due to the whole ruckus about holidays and what-not.)
I remember on some old covers there was only the 'published date' so you have to take this 2 weeks delay into account if you are interested in the date it was out. I guess it iS something similar why issue 1 is on december...
It's somthing inherited from old times, when distribution was expensive and slower. One is for the "release" date and the later is the deadline for return the issues that were not sold. In this case, this issue comes out on October 1st, and the retailers should be able to give back the unsold issues until October 15th. The "official" release date is usually referred to the last one, but nowadays is certainly inaccuracy.
the october version of monthly magazines comes out in september. the same thing if with financial reports of the year that doesn't happen at the end of december. nintendos fiscal years goes from march to march, which sounds ridiculous but thats how it is.