Passive DNS [2] has been in my toolbox for 15+ years, and is invaluable for security research / threat intelligence. Knowing historical resolutions to something are so helpful in investigations.
For anyone interested, they should check out the talk by one of the DomainTools people [3] on how it can be utilized for investigation.
Are you passively collecting this data, or actively querying for these records?
[1] - https://www.domaintools.com/products/threat-intelligence-fee...