D7 started off as an internal project for a Marketing Agency more than 5 years ago. When it started we used 3 or 4 sources depending on the search. Since then this has vastly grown and we source data from over 100 different locations (and growing).

The important thing we do is cross reference the same data that our systems find in multiple sources before trusting a piece of data.

Say for example we we find a new telephone number for Jims Widgets Inc. - we don't assume that this is the correct phone number until we come across the same phone number for Jims Widgets Inc. in multiple locations. Any data suspected to be bad is dropped.
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