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Google indexes index page of a section ( call it articles ) i.e available in header tab. But never indexes the links that are present in that section.
I tried Google Site Maps, and also mod rewrite function to convert article.php?catid=12 to /why_this_page_is_not_indexed_12.html
But no use. those pages never got indexed.
Thanks in advance.
Basically when the freshbot finds a page for the first, that only keeps it in the index a day or two.
Not much to worry about in this, other than you will need to keep new pages linked from a main page longer to get them truly indexed sooner.