lucy24 - 7:17 pm on Jul 25, 2012 (gmt 0)
Short answer: the word 'noindex' is not part of the Robots Exclusion Standard. Use it at your own risk.
Disallow = robots stay out, no crawling allowed
Noindex = page is not mentioned in google's* search index
Yes, a page can be indexed even if a search engine has not seen it. They only have to know it exists.
* I say specifically google, because That Other Search Engine has indexed a few pages that are clearly and explicitly labeled noindex.