I'd never thought of such a problem in the whole SEO spectrum before I considered launching my own website.
Imagine that I have a website which is updated once per month and Google spider knows about that. So what happens if I've updated one of my pages with new content just after it was crawled? Do I need to wait for a month before Google spider will come back? And is it possible that someone can find my website by queries which are not already relevant to it?
Has anybody encountered such problem or has a solution?