Where are the feeds of sold domains?

[zachbb]

Background:
There are multiple websites which record recent domain sales. A few of them are here:

• Domain Tools: https://www.domaintools.com/buy/sales-history/
• NameBio: http://namebio.com/
• DN Sale Price: http://www.dnsaleprice.com/

And a user here on NamePros who posts (I think automated) sales reports:
https://www.namepros.com/search/1808163/

Question:
Where do these sites get this data from?

I know that Sedo has the following RSS feed of recently sold domains:
https://sedo.com/rss/rss_list.php?rss_id=17

I don't see where Afternic or GoDaddy Auctions, or NameJet list these sales.. Any idea where this data is collected from?

 

[DomainBELL]

and DNJournal.com