Hm, there might be other sites out there -manga research is not my forte XD- but you can try http://mangaupdates.com. That's the place I go to for all the manga info I need.
These entries should answer a few of your questions: http://www.mangaupdates.com/series.html?id=342 X 1999 http://www.mangaupdates.com/series.html?id=341 xxxholic
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These entries should answer a few of your questions:
http://www.mangaupdates.com/series.html?id=342 X 1999
http://www.mangaupdates.com/series.html?id=341 xxxholic