How and when does the tracking of shared links work?

Question

My two main questions:

1. Are all URLs that include your User Id tracked?

2. Can the visitors who use the tracked URLs have Stack Exchange accounts?

Specifically:

Recently the ability to earn badges for sharing links to posts on Stack Exchange sites was revealed.

I'd like to know when and how this tracking works.

It's clear that if you go to a question, and make use of the link button, you will get a URL with your User ID that will be tracked if a visitor uses it to get to SO.

For example, let's use this question as an example. It's regular URL is:

https://stackoverflow.com/questions/309300/defend-php-convince-me-it-isnt-horrible

If you go to that page and use "save link as" in the link section of the question you will be given a tracked url with your User ID:

https://stackoverflow.com/q/309300/[USER ID]

My question is, are there other URLs that would be tracked?

All of the following URLs take you to the Question / Answer, but are they tracked?

For example what if I just tack my User ID onto the long url?

https://stackoverflow.com/questions/309300/defend-php-convince-me-it-isnt-horrible/[USER ID]

What if I add my User ID to an answer URL?

https://stackoverflow.com/questions/309300/defend-php-convince-me-it-isnt-horrible/309622#309622/[USER ID]

or even

https://stackoverflow.com/q/309622/[USER ID]

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Is there a way to know that a URL is being tracked? Is there some sort of format to follow? Are the only tracked URLs the ones provided in the Question links?

Finally, does this sentence from the blog post mean that visitors cannot have an account?

Also, the tracked IPs must originate from outside our existing network.

Answer 1

Only the form of the link provided by

1. Facebook icon
2. Twitter icon
3. Link below post

is tracked, Namely:

http://{domain}/q/{question-id}/{user-id}
or
http://{domain}/a/{answer-id}/{user-id}

No other link form is tracked. Period.

It doesn't matter whether incoming visitors have an account or not, what matters is that the IP is unique and the shared link was clicked outside our network.

Note: Answer-specific short URLs were not originally tracked, but support was later added.