How to sign up for archive.org/download/project-name

Why isn't the site I'm looking for in the archive?

Some sites may not be included because the automated crawlers were unaware of their existence at the time of the crawl. It's also possible that some sites were not archived because they were password protected, blocked by robots.txt, or otherwise inaccessible to our automated systems. Siteowners might have also requested that their sites be excluded from the Wayback Machine. When this has occurred, you will see a "blocked site error" message. When a site is excluded because of robots.txt you will see a "robots.txt query exclusion error" message.

The exclusions are at the choice of siteowners or due to take-down notices. I'm afraid if you are asking whether you can decide to include what is presently excluded the answer is that you cannot (for other than your own site/s).

It's a bug in the Wayback Machine, inserted in 2010.

It's now fixed in the current Wayback Machine, and also our next-gen Wayback.