Hi! My name is Erin, and I'm on the Moz Help Team. Great answer by the way, Paddy! I just want to throw in a little more information about Just Discovered Links (JDL).

All of the links that end up in JDL come from tweeted bit.ly links. We get our data for that tool from bit.ly and they can provide us with what the associated full link is, which is how we show the full link in the tool (because the bit.ly version of the link wouldn't be very informative), but all of the Just Discovered Links come from URLs that were tweeted as a bit.ly.

Basically, if someone tweeted the page http://www.squaresocial.co/site-isnt-ranking-google-anymore/ as http://bit.ly/1jyxEpX, bit.ly would see the tweet and let our system know that A. the URL http://bit.ly/1jyxEpX was tweeted and B. that that bit.ly URL redirects to http://www.squaresocial.co/site-isnt-ranking-google-anymore. Our system then crawls the page http://www.squaresocial.co/site-isnt-ranking-google-anymore to see where that page is linking and we can see there is a link to moz.com on that page, so we include it in the Just Discovered link index for moz.com as the full URL, rather than the shortened version: http://screencast.com/t/fVs59BsYE6rT

I hope that helps!

Erin