Just in Case if you want to know how Licensing Process is:
taken from local Publisher FAQ in my Place
The Process to Published manga is relative long, due to many processes that require approval from the original publisher, or even the mangaka itself. both of the process in the form of chapters in manga magazine or the tankoubon.
If your place also licensing the manga magazine (Shonen Jump, Magz, or Star). the tankoubon will be longer to released since the policy it self requiring that the magazine must released the latest chapter before the tankoubon.
ex: if your place already licensing Naruto till volume 50, The magazine will released the number after that, or maybe start from chapter 1 again, (I'm not sure) but the released of tankoubon will delayed until some time.
In Japan the gap between the average volume of 2-6 months, sometimes more.
This series depends on how many pages per chapter that was published in the Japanese comic magazines and also depends on the manga magazine published weekly, biweekly, or monthly.
If a chapter has 32 pages and a comic takes around 200 pages, then a tanko (short for tankoubon / comic unit) took sixth chapter. If a comic magazine just published a chapter / month, then at least 6 months to collecting enough material for one tankou;and the fastest is 1.5 months if the magazine was published weekly.
And remember, that if a chapter 32 pages, there are some comics that the number of pages is less than that.
Then after that, this material will be published as they process tankobon in Japan. (still in Japan)
after the tankoubon released in Japan, Japan Publisher will send the raw to Publisher in your place and then still have to be processed again here, including the permitting process contents to be printed which must be authorized Japan each volume (where the process what MOST LONG is awaiting approval print / approval contents and cover from Japan ).
In addition, the representative agent in the Japanese publisher and editor in each country who are responsible might not only deal with a series title or an issuer that is all alone, but there are so many series and other publishers are handled. So the handling and preparation of the manuscript published schedules are also interspersed with intervals other series.
Why sometimes there are comics that stagnates at a certain number?
that because Permission granted by the original publisher's sometimes a certain amount of volume, not directly to the end. After the license renewal process will be processed again.
Trivia:
there are publishers who requested approval to send over and over again just because retouch comic panel should be done very carefully to not touch some object even only for one millimeter.
there are publishers who could ask for approval to send repeatedly only to control the color of a picture illustration
there are editors who have to outline around each piece of specific comics, just to check out his comic edge there should be a certain distance with millimeter size, so the results can meet the standards of one of the Japanese publishers
there also mangaka who doesn't want their manga released outside Japan, or only for some country
note: this only for hard copy manga