Can you potentially point me to a reliable source for this type of number (or tell me how to calculate it myself, assuming I can get the zone file from Verisign

Can you potentially point me to a reliable source for this type of number (or tell me how to calculate it myself, assuming I can get the zone file from Verisign)? I had similar issues with the data, and I tried emailing these guys to find out more about their methodology. Didn't get a response. Are they crawling DNS for every domain that has changed info (or is new, or drops) from the prior zone file? How would one recreate this data, hypothetically? EDIT: I'm aware of the ICANN delayed data (as the site below uses), but I am hoping for a more up-to-date source.