Are pilots produced but not released?
Not really, since Most anime's are based on popular manga's already published.
Making a pilot in the US is byproduct of creator's who try to push their show to producers and executives.
If the manga is popular, the anime will no doubt be successful. This is not always the case in the US and Japan. &quot;The Big O&quot; was a miserable failure in Japan, but in the US was well received.