>While exploring an area I found something that looks like the
>solution for a riddle but I didn't find the riddle itself.

Could be nothing. :)

>So my question is: Is the riddle in the same area?

Most commonly, but not always.

>Are all
>areas "consistent" in itself in that matter or is it quite
>possible that I have to look in different areas of the same
>(or of a different) author?

I've definitely written quests and stuff that involve my areas and also involve other areas. Probably, other people have done the same.